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By Henry Howe

W. E. RUDER, Schenectady, N. Y.-In 1913 I presented a paper before this society on Grain Growth, and at that time it seemed to me that the only explanation for grain growth was that of critical strain. I do not think I published the photographs at the time, but I made some experiments on the effect of stretching sheets of metal. This allowed for fairly accurate determinations of the amount of cold deformation, At the time I worked-with silicon steel because one could see the change in grain growth with the naked eye. I stretched about 10-samples from 0.5 per cent. to 10 per cent., and, after heating to 1,050° C., I found that the maximum grain growth occurred at about 2 ½ per cent. cold deformation. This I designated "the critical strain" for maximum grain growth. About a year ago I talked with Prof. Jeffries, who explained to me his ideas of grain growth. It occurred to me that it would be a very easy thing to check the strain hypothesis against the strain and temperature hypothesis, if we took a certain number of these strips, strained exactly alike and heated to different temperatures; in that case the maximum grain growth ought to appear at a different percentage of deformation for each temperature. These experiments showed that there was, as Mr. Jeffries shows in his present paper, a decrease in germinative temperature with increased cold deformation. The samples were stretched from ½ to 8 per cent. and heated for 10 hr. in hydrogen. Samples were introduced into a furnace previously heated to temperature. A maximum grain growth was obtained at 5 per cent. deformation, when heated to 750° C.; at 2 ½ per cent. when heated to 800' C.; at 1 1/4 per cent., if heated at 950°C.; and at 5/8 per cent.. when heated at 1,100° C. This shows very clearly that the germinative temperature decreases with the increase in cold deformation. The growth was very much more marked, however, at the high temperature, i.e., the grain grew more rapidly and attained a much larger size than at lower temperature. In considering the photographs (Fig. A) those along the lateral edges should be ignored because.

Jan 4, 1917

By W. J. Sharwood

The assay or estimation of the total gold content of an ore presents little difficulty, when circumstances permit of securing a thoroughly representative sample. The general practice has been fairly standardized, and such errors as occur in the results obtained are for the most part attributable to the methods of sampling rather than to those of assaying, while duplicate assays made by skilled workers usually agree closely. When it is a question of estimating the "free" or amalgamable gold of an ore, as opposed to the total gold, there is but little uniformity in the methods employed by different workers, and often equally little in the results obtained when duplicate determinations are attempted, no satisfactory standard method having been generally adopted. The methods in use are of two general types—"panning" and "amalgamation." Panning For the estimation of the value of the visible gold by panning or washing, a weighed sample may be taken, ranging from an ounce to several pounds; a kilogram or 2 lb. is a favorite quantity for laboratory tests, while a prospector often uses a full miners' pan, say nearly 20 lb. or 10 kg. In the case of rich quartz, ground to about 30 or 40 mesh, a Mexican horn is convenient, using 1 to 8 02;. of material, and a 6-in. frying pan is favored by many prospectors in dry districts. Bateas, plaques, and dishes of various patterns are used for the same purpose. With these, fairly close results may be obtained by using for ocular comparison standards consisting of weighed amounts of gold of similar character as regards purity, fineness of division, and the general shape of the particles, which standards are preferably obtained from gold of the same locality, or the same deposit, as the ore or gravel being tested. Men working in one particular district sometimes become surprisingly expert in thus judging the value of an ore by the eye, the weights of both ore and gold being guessed. On the other hand, many have been led to overestimate the value of ore and gravel from unfamiliar localities, where the gold has been very finely divided or of unusually high silver content, and a novice may

Jan 1, 1916

By Charles Stuart

A PAPER on this subject can cover but a limited range. A thorough visualization of the subject would contemplate a comparative analysis of haulage machines and batteries of various types; the relationship of the storage-battery locomotive to other types of mine haulage should be considered and limiting factors in each case should be carefully developed. This paper will briefly deal with these factors. So far as the writer has been able to determine, the first storage-battery locomotives for mine haulage were manufactured in 1897 or 1898 and were tried out in the Pocahontas coal field, but they were not sufficiently satisfactory to justify their continued use. Battery explosions were frequent and caused serious damage to the wiring, electrical equipment, and the clothing and bodies of the motormen. Sulfuric acid was used as the electrolyte. Experiments were then conducted with locomotives bearing reels of flexible cable through which connection between the motors of the locomotive and the trolley wire was maintained. At first, these reels were turned by hand. Later, the reels were revolved by contact with the wheels of the locomotive, being raised out of contact with the wheels, by a lever, when necessary. About 1902, the plan of operating the reel, by chain and sprocket wheels, from one of the locomotive axles, as is still the practice, was devised. The popular floating motor-driven reel had its inception in the Pocahontas fields prior to 1906. The maximum radius of operation of the reel-type locomotive is about 500 ft. (150 m.) from point of connection with trolley wire. This is ample for room work and certain entry work, but the need for a machine that would operate entirely independently of the trolley wire was so great that, with the development of the storage battery, renewed efforts were made to manufacture a successful storage-battery locomotive. About 1908, the gasoline locomotive was introduced. In spite of many objections to this type of machine for such work, the fact that hun¬dreds of these machines were purchased was proof of the need for a machine operating independently of the trolley.

Jan 1, 1922

By C. E. Mendenhall

THE word temperature has both a colloquial and a technical use. For everyday purposes of abusing the weather man, no very exact definition is necessary, but for the purpose of giving a simple summary of the physical laws that form the basis of practical pyrometry, something more precise is required. Beginning, therefore, with the common concept of "hotness" and "coldness," we must agree on a method of measuring differences in "hotness," on the unit to be used, and on the point from which measurements are to be taken. We shall then have a definite "scale of temperature," which can be used in all methods of pyrometry. But, as in many similar cases, it is much easier to define or describe something than it is to make practical application and use of the definition; so that much of our attention will be taken up with practical methods of realizing or applying the scale agreed upon. It was early observed that changes in temperature produced large and easily measurable changes in gases, which may be most simply separated into changes in volume (expansion and contraction) under conditions of constant pressure, and changes in pressure under conditions of constant volume. These changes are much the same in magnitude for the common gases oxygen, nitrogen, and hydrogen and also for the rarer helium and argon. This relative uniformity in behavior led to the suggestion of "the gas thermometer" and "the gas scale" as the basis for all temperature measurements. However, as methods were refined, differences appeared between different gases and different ways of using gases, so that Lord Kelvin introduced his more fundamental notion of the "absolute thermodynamic scale" of temperature, which he defined as follows: Given two bodies, say two tanks of water, at different temperatures to determine these temperatures on the "absolute thermodynamic," or Kelvin, scale, operate a thermal engine between these two temperatures, letting it take in heat from the hot body and give out heat to the cold, which therefore corresponds to the boiler and the condenser of a steam engine. The engine we may imagine as a cylinder and piston inclosing a gas and operating with the well-known Carnot or isothermal-

Jan 9, 1919

By C. O. Brawner

The advent of larger drilling, excavation, and milling equipment is resulting in a tremendous increase in the scale and annual tonnage of open pit mining. At the present time, open pits up to 3000 ft. deep, and tailings dams and waste dumps up to 600 ft. high are being planned. One of the major problems that projects of this magnitude create is stability. Stability at open pit mining developments must be assessed for tailings dams, waste dumps, and open pit slopes in overburden soil and in rock. Soil mechanics principles are used to assess the stability for the first three. This science was developed by Dr. Karl Terzaghi in the 1920’s, and since that time the theories and principles have been tested and evaluated. This experience has resulted in the development of sound theoretical concepts, workable sampling and testing techniques, and accurate methods of analysis. Typical problems that can be analyzed include: -bearing capacity of soil under dams and waste dumps. - amount of seepage under and through dams. - stability of slopes and determination of safe slope angles for tailings dams, waste dumps, and open pits. - influence of earthquakes on stability. - influence and cost of different excavation and construction techniques. To assist in comparing engineering experience, an international soil classification system has been developed and used for several decades. In addition, many excellent text books are available outlining soil mechanics principles and techniques. A high degree of technology exists in soil mechanics. This, the mining engineer cannot afford to ignore. If soil mechanics principles had been applied, many major failures involving tailings, tailings dams, or waste dumps, such as those at Aberfan, Mufulira, Luanshya, and El Cobre would not have occurred. Tailings dams are planned in Canada that will be up to 600 ft. high. Construction procedures used in the past have paid little attention to the compaction of the shell material or to the influence of earthquakes on stability. This neglect has led to failures. While failures in low dams may not be too serious, for high dams such failures could have catastrophic results. Another major area of concern is the stability of rock slopes. From the standpoint of long

Jan 1, 1971

By T. S. Lovering

An economic geologist is concerned primarily with finding deposits of economic value, estimating their tenor and quantity, their shape and position. Thus the primary problems can largely be lumped under three headings: position, character and quantity; and all three are phases of the broader problem of genesis. Distribution, tenor and quantity are of immediate practical importance and are studied constantly by all who exploit mineral deposits. Although the emphasis changes from year to year, the problems of genesis seem more remote and rarely get the serious consideration from the field man that the other three do. Our understanding of the problems of the genesis of mineral deposits has come largely as a by-product of more evidently utilitarian work in the past, and probably will continue to grow in the same manner lor many years to come. However, it might be economically fruitful for the producers to have many competent investigators spending their time chiefly on the problems of genesis of mineral deposits. Many years ago, when first engaged in work for the United States Geological Survey in Colorado, I expressed a conviction which was just then dawning on me by saying that economic geology was turning out to be 80 per cent structural geology, to which Mr. B. S. Butler replied, "Yes, and more than 80 per cent of structural geology is lithology." At the present time there seems to be a widespread feeling among economic geologists that the problems of position or distribution are largely problems of structure and rock types. Types of Research Ptesearch in any branch of geology can be conveniently divided into two types: field research and laboratory research. Ideas are usually dug up in the field, pruned or developed in the laboratory, and taken back to the field for proving. For either the first or last step the field data should he as complete as possible, and the structural geology of nearly all our mineral deposits still needs more detailed delineation. In general, this means mapping on larger seales. Ideally the structural map should give a factual picture of a11 visible effects of stress; there is still room for vast improvement in the technique of presentation. Information that is much

Jan 1, 1940

By T. S. Lovering

An economic geologist is concerned primarily with finding deposits of economic value, estimating their tenor and quantity, their shape and position. Thus the primary problems can largely be lumped under three headings: position, character and quantity; and all three are phases of the broader problem of genesis. Distribution, tenor and quantity are of immediate practical importance and are studied constantly by all who exploit mineral deposits. Although the emphasis changes from year to year, the problems of genesis seem more remote and rarely get the serious consideration from the field man that the other three do. Our understanding of the problems of the genesis of mineral deposits has come largely as a by-product of more evidently utilitarian work in the past, and probably will continue to grow in the same manner lor many years to come. However, it might be economically fruitful for the producers to have many competent investigators spending their time chiefly on the problems of genesis of mineral deposits. Many years ago, when first engaged in work for the United States Geological Survey in Colorado, I expressed a conviction which was just then dawning on me by saying that economic geology was turning out to be 80 per cent structural geology, to which Mr. B. S. Butler replied, "Yes, and more than 80 per cent of structural geology is lithology." At the present time there seems to be a widespread feeling among economic geologists that the problems of position or distribution are largely problems of structure and rock types. Types of Research Ptesearch in any branch of geology can be conveniently divided into two types: field research and laboratory research. Ideas are usually dug up in the field, pruned or developed in the laboratory, and taken back to the field for proving. For either the first or last step the field data should he as complete as possible, and the structural geology of nearly all our mineral deposits still needs more detailed delineation. In general, this means mapping on larger seales. Ideally the structural map should give a factual picture of a11 visible effects of stress; there is still room for vast improvement in the technique of presentation. Information that is much

Jan 1, 1940

By D. J. Salley, M. Burke, G. L. Simard

A PREVIOUS paper1 described experiments on the interaction of dithiophosphate with galena and suggested that the process had characteristics of both chemisorption and surface chemical reaction. In order to add to this knowledge, a study has been made of the competition of a second ion with the dithiophosphate for a galena surface. Use again was made of radiotracer methods. Since radiophosphate was readily available, it was chosen as the competing ion. It is a feature of the tracer method that, in spite of similarity in the chemical behavior of the ions, the measurement of one ion in the presence of another can be made as simply as if only one ion species were present. In order to study the competition effectively, it naturally was necessary to examine the interaction of phosphate with galena alone as well as in the presence of dithiophosphate; consequently, this report consists of two parts. The first is devoted to a study of the rates, the isotherms, the desorption, and the exchange in the phosphate-galena system in the same manner as was done for the dithio-phosphate-galena system. The second portion is concerned with the studies on the competition. Flotation experiments on the three-component sys- tem are also outlined and the relationships involved are discussed briefly. The experimental method was that of the previous paper. The preparation of the galena, the radioactive and the nonradioactive dithiophosphate, and the procedures for radioactive counting, for sorp-tion, and for flotation measurements were identical to those previously employed. The radiophosphate* was used in the form of disodium phosphate solution. In the competition experiments the effect of the phosphate ion in depressing dithiophosphate uptake was followed by holding the initial concentration of nonradioactive phosphate constant while varying the initial concentration of the radioactive dithiophosphate. Counterfashion, the depression of phosphate by dithiophosphate was obtained by keeping the initial nonradioactive dithiophosphate ion concentration constant and altering the initial concentration of the radioactive phosphate ion. All solutions were buffered at a pH of 7.8 a0.1 by 20x10-' mol per cc of sodium carbonate. Measurements with radiocarbonate indicated that little or no carbonate could be sorbed in the presence of

Jan 1, 1952

By S. F. Urban, G. Derge

AT the time this investigation was initiated variations were observed in the quality of different heats of basic electric-furnace steels, although they had been made under purportedly similar conditions. This indicated that these variations were related to normally unobserved variations in the character of the bath, especially during the "refining" period. Although the slags used for this operation are commonly referred to as "reducing" slags, and are regarded as having a "deoxidizing" action on the bath, no reliable measurements of this action were available. It was decided, therefore, to study the behavior of oxygen in the metal for a large enough number of heats to learn its normal variations and to relate these variations to regularly observed conditions [f] operation. The most important general conclusion reached was that the time a heat is held under a reducing slag should be reduced to a minimum, which was about an hour and a half under the conditions studied. Beyond this time no observable beneficial effects are obtained from the reducing slags, insofar as oxygen and sulphur content of the bath are concerned. It is likely that added time may increase hydrogen content as well as heat costs. The oxygen content of the bath is never reduced below the amount in equilibrium with the carbon. Concurrently with this work, J. S. Marsh1 presented data that supplement and support many of the results of this paper. PROCEDURE The work was done in two different electric-furnace shops of the same plant. The selection of heats was made primarily with regard to the convenience of heat schedules. Companion slag and metal samples were taken just prior to slag-off and throughout the refining period for an initial set of 17 heats, and before slag-off and near tap for an additional 13 heats. Slag sampling presented no particular problem; a spoonful of slag was poured onto a metal plate and when sufficiently cool was sealed in an airtight container. Sampling the metal for oxygen presented a more complex problem. Because of the lack of previous experience in sampling electric-furnace baths, a number of methods were compared. Chilled Wedge Samples2 An unkilled metal sample is removed from tie furnace in a well-slagged carbometer spoon and poured immediately into a heavy copper mold designed to provide rapid freezing. Three different types of molds were used to determine the optimum for electric-furnace heats. The Big Wedge Mold (a) was a 4 by 4 by 4-in. split copper mold, yielding a wedge-shaped casting 1 in. wide, 1 ½ in. long, and ¼ in. maximum thickness, and was finally adopted as the most satisfactory design. The Long Wedge Mold (b) was a 2 by 2 by 5 ¼ -in. split copper mold, yielding a wedge-shaped casting 1 in. wide, 2 ¾ in. long, and ¼ in. maximum thickness. The Small Wedge Mold (c) was 2 by 2 by 4-in. split copper mold, yielding a wedge-shaped casting 1 in. wide, 1 ½ in. long, and ¼ in. maximum thickness.

Jan 1, 1947

By Harvey S

After considerable experience in connection with the magnetic iron-ores at the South, especially in the Cranberry district of western North Carolina and eastern Tennessee, the writer was led into a thorough investigation of the magnetic separation of iron-ores, and, from this investigation, has gradually been developed a separating machine which it is the purpose of this paper to explain. Numerous United States patents have been issued upon machines for magnetic separation. Since the original patents date back to 1849, it is not possible to-day to establish broad claims upon the principles of electro-magnets as applied in such machines. Among these inventions there are certain types of separators which have very marked practical advantages over the others; and these successful machines, while varying radically from each other in their proportions and arrangements, are all based upon a principle originally explained in a patent which was granted in 1870, and which has now expired by limitation. The problem of practically separating iron-ores, as found in the mines, is very different from the separation of a purely magnetic substance from a purely non-magnetic one, since the crystals of magnetite, scattered through the ore-bearing rock, and sometimes collected in masses, are of very different sizes. The average size of the particles may be definitely ascertained for each mine, and the crushing- and screening-machinery may be adapted thereto, but there will still be a large percentage of very fine crystals which, in the crushing for the average, will not be broken apart from the gangue. If these mixed particles are thrown into the heads they carry gangue with them, and if thrown into the tails they occasion a loss of ironore. There are two methods for preventing such loss. One is, to crush all the material to the size of the finest particles, which means, of course, a large crushing-plant, heavy wear and tear, and excessive cost for repairs, and the production of only a very fine-grained concentrate which our blast-furnace managers, to say the least, do not

Jan 1, 1893

By F. Keller, E. H. Dix

The desirable high strength and hardness of the heat-treated strong aluminum alloys result from two distinct structural changes: (1) the formation of a solid, solution by heating at the required temperature for a sufficient period, and the substantial retention of this solid solution by rapidly quenching; (2) precipitation of particles of constituent and coalescence to a critical size to produce maximum strength and hardness. In alloys of the duralumin type, that is, alloys containing both copper and magnesium silicide precipitation takes place at normal atmospheric temperature, whereas in alloys containing copper without magnesium silicide or magnesium silicide without copper, maximum properties are obtained only after an accelerated aging treatment consisting of heating for 15 to 20 hr. at temperatures of about 150" C. The mechanical properties of these alloys subsequent to quenching but prior to aging are ideal for forming operations. Unfortunately, however, the alloys of the duralumin type age very rapidly during the first 24 hr. and aging is substantially complete after four days. For severe forming, such as the heading of rivets, it is desirable that this be accomplished within ½ hr. or at the most 2 hr. after quenching. Alloys containing magnesium silicide without copper also age at normal temperatures but the aging is less rapid and the material can be satisfactorily worked within several weeks after quenching. Some slight aging of alloys containing copper alone also takes place at room temperature but it is unimportant from the standpoint of workability. Any method of retarding the aging at room temperature of the duralumin type of alloys would be of considerable advantage in that the period during which the material could be worked successfully would be lengthened. For instance, in aircraft plants it is customary to supply the workmen with small lots of rivets that should be used within ½ hr . after heat treatment. Such procedure has the obvious disadvantage of being uneconomical, and furthermore there is always the possibility that the workmen would use the rivets after the time limit had expired, or the supply being depleted might use some that had not been heat-

Jan 1, 1931

By F. A. Harvey

DURING the last few years, there has been a constant tendency toward increasingly high temperatures in many lines of industry. The necessity for increased production of coke gave a 16-hr. coking period where we used to have 24 or even 30-hr. periods. Mechanical stokers have increased the temperatures in boiler furnaces. The use of a chain-grate stoker with coke-breeze fuel necessitates a low arch in the furnace and temperatures run much higher than firebrick were formerly called upon to stand. These higher temperatures have necessitated more rigid tests and the separation of even high-grade firebrick into separate classes. More severe tests mean higher temperatures and closer control, and this, in turn, means better pyrometer tubes. Platinum couples do not have a very long life when used at temperatures exceeding, say, 1200° C., but the proper selection of a high-grade brick to be used in a-boiler setting will save the cost of several couples; and with freight rates continually increasing it becomes increasingly important to know where brick may be bought, nearest the job, that will prove satisfactory. Couples that will stand continuous use at higher temperatures, of tungsten, molybdenum, or other metal, will doubtless be forthcoming as soon as the need becomes sufficiently urgent. There are on the market several tubes that are entirely satisfactory for temperatures up to 1300° C., if properly protected from heat shock. The Semet-Solvay Co. makes a practice, however, of testing silica and clay firebricks at 1450° C. for 72 hr., and so far we have been unable to find a tube that- is entirely satisfactory for this purpose. A graphic record of the temperature during the entire test is extremely desirable and hence we have been trying out anything that gave promise of success. Several years ago we were using insulating tubes, made purely for electrical work, of vitrified porcelain. These tubes stood up under any temperature we were able to reach and were apparently impervious to gases. When this stock gave out, due to mechanical breakage, we tried other insulation tubes only to have them melt down like glass. Marquardt Masse tubes were tried next under a statement from the distributors

Jan 9, 1919

By Henry P. Ehrlinger

The Alta and St. Louis mines of the Alta Mines, Inc., produce a somewhat oxidized ore with a talc gangue that presents quite a problem in milling. For several years the mill recoveries were relatively low and there seemed to be no cure for this condition even with increasing the various collecting agents and frothers to two or three times of what they should be. The usual alibi of "oxidized ore" was given as the reason for these results and the matter stood there for some time until these investigations were started. Flowsheet As a brief outline of the flowsheet the ore is crushed to minus I in. in a Telsmith jaw crusher and then fed to a 64½ Marcy grate mill. The resulting product from the grate mill is passed over a trommel where the coarse particles (plus 7 mesh) are returned to the grinding circuit through the classifier. The under 7-mesh pulp is passed over two Denver mineral jigs where a high grade concentrate is produced, thence over two Wilfley tables where a table concentrate is produced and about 80 pct of the oxide lead recovered. The tailings from these tables are pumped back to the classifier and after classification the 30 pct pulp density product, which overflows the lip, is passed into a series of 10 Denver economy flotation cells where a lead-copper concentrate is produced. Three products are made and shipped to the smelter termed jig, table and float concentrates. Results with various Reagents In March of this year work was started on the metallurgical problems of the mill and, as is shown in Table I, the results obtained were not too efficient. Tests were run with various reagent combinations that were recommended for ores of this nature but there was no appreciable effect on the recoveries. The grades of the flotation concentrates were reduced by the insoluble picked up and retained by these more powerful collectors and frothers. Results with "Metso" In past work on ores of this type the use of "Metso" had improved gold and lead recoveries, but no effect on the silver and copper recoveries had been noted. To

Jan 1, 1949

By Richard D. Divine

In the Parkes process of extracting precious metals from lead, zinc is added to the molten lead containing gold, silver, copper, and some antimony. These metals, with the exception of antimony, form an alloy with the zinc by reason of their greater affinity for it than for the lead, and this alloy, being lighter than lead, rises to the top, carrying the precious metals with it, whence it can be removed by skimming. These skimmings are further treated for the separation of the zinc therefrom, and the recovery of the precious metals, the zinc being driven off by heat and again used for another operation. In addition to the zinc that combines with the silver, etc., a certain amount is necessary to saturate the lead, and it is therefore necessary to treat the desilverized lead to free it from this residual zinc. TO do this it is heated again in a reverberatory furnace and air or steam is blown through it. This oxidizes the zinc together with a small amount of lead and antimony, leaving the lead free from zinc and antimony, and forming oxides of these metals, which rise to the top and are skimmed off. This process relates to the separation of the metals in these oxides or skimmings. The skimmings are cooled, crushed, and mixed with carbonate of soda and pulverized oil coke. The mixture is heated in a reverberatory furnace on a bath of lead, to about 1,000" C. The metals are reduced by the coke, the lead and antimony go into the lead bath, while the zinc is volatilized and burned to oxide. This impure oxide is at the present time treated at Omaha by the Hall process of electrical precipitation, making a very pure metallic zinc. It can also be very easily refined by the old Schnabel process of using ammonia and carbon dioxide as a solvent. It seems to be in an ideal form for this purpose, and very few changes from the original method are required to obtain the zinc oxide practically C. P., leaving the lead and antimony as residues. There has been considerable difference of opinion regarding the effect

Jan 1, 1915

By Roswell Johnson

ALL strata not yielding oil or gas in commercial quantities or a corresponding amount of water may be called dry in a wide sense. In petroleum geology,, however, we may exclude all sands of too low or fin porosity to yield gaseous or fluid contents to the hole drilled in the sand before any original pressure that its contents may be under is disturbed. Most rocks are of this class and they are not reservoirs in our definition; their "dryness" is wholly a matter of course. What are the contents of the pores or what is the exact porosity of such rocks is of almost no concern to us, for economically they are "dry." What does interest us is the content of a rock having sufficient porosity and the pores of sufficient size to yield oil or gas in commercial quantities, if they were present under original pressure: Dryness of these reservoirs is a matter of supreme practical importance. Three views current as to such dryness seem, to me, to apply in a few cases only. It is the purpose of this paper to give reasons for this position and for believing that, in ordinary sedimentary rocks, there is only rarely a reservoir of competent porosity and undisturbed pressure that is dry in the sense of not yielding water, oil, or gas when first penetrated. 1. Gardner1 writes of some Kentucky sands, "There has never been present any salt water or other water in the sand." Absence of water cannot demonstrate this position. It is necessary to show that the rocks were not laid down in water, but in air, and that they became so enclosed, while still above the water-table of the, ground water, that water has not been able to enter since. Most of these sands, and certainly the productive limestones, were deposited in water; and such sands as have been commercially productive show no reason for believing that the overlying shale or limestone was not laid down progressively from one direction and in water that would have flooded it. No adequate explanation has been offered for this hypothesis, which is so inherently improbable.

Jan 1, 1920

By E. E. Thurlow

The Geology Div. of Northern Pacific Railway Co. has adapted to its exploration efforts field procedures for geochemical sampling and semi-quantitative analysis which have been developed through research by the U. S. Geological Survey. The sampling is done in conjunction with reconnaissance geologic mapping on aerial photographs or during field checking of maps which have been prepared largely by photo-geologic interpretation. Stream sediment or soil samples are taken and readily soluble combined heavy metals are extracted with ammonium citrate followed by colorimetric titration with dithizone at the sample site. The effectiveness of this approach has been demonstrated both in positive and negative results, thereby assisting in the elimination of large areas of land from further immediate attention and in providing targets for followup exploration. An occa sional sample is submitted for spectrographic analysis as a check on the possible presence of other elements of economic significance. Field laboratory procedures are also being implemented for determining molybdenum, mercury, and other metals which may be valuable in themselves or useful as pathfinder elements in outlining mineralized areas. A lead-zinc occurrence in Oregon and a copper deposit in Montana were readily detected and outlined by stream sediment and soil sampling and a heavy metal anomaly that lacks obvious interpretation has been found in northwestern Montana. Detailed mapping and additional sampling are followed by other exploration techniques if warranted. Northern Pacific's program of reconnaissance mineral evaluation of company-owned lands and adjoining areas was outlined in a paper presented at the American Mining Congress meeting in Las Vegas four years ago. That report included policies and procedures with respect to mineral development on Railway Co. lands and may be referred to for information on these matters.1 In a sense this paper is a progress report on the use of geochemical prospecting in Northern Pacific's continuing mineral evaluation program. At this time there are positive results but as yet there is no real success story in the form of a minable ore body. GEOCHEMICAL PROSPECTING PROCEDURES The decision to use geochemistry as a reconnaissance exploration tool must be followed by research into sampling and analytical methods and into the interpretation of results. Various analytical methods were tried and evaluated by the Geology Div., including hot and cold acid extraction with and without fusion of the sample, panning and magnetic separation followed by dithizone testing of the magnetite, and cold aqueous extraction of metallic ions followed by indicator tests. Samples were first sent to the laboratory for analysis; later field laboratories were established and now virtually all testing is done at the sample site. It was concluded that, where applicable, the quickest dependable methods for reconnaissance use are the dithizone field tests for readily extractable heavy metals. This involves the simultaneous treatment of a sample, usually of soil or stream sediment, with two immiscible liquids; one a cold aqueous extractant (ammonium citrate) and the other a solution of dithizone in toluene or xylene.2 Dithizone is a colorimetric indicator that reacts quantitatively with copper, lead, zinc, and several other metals to form colored complexes in organic solvents. Results may be expressed in ml of 0.001 pct dithizone that are required to reach the blue end point, or calibration of the test results can be carried out with standard solutions of zinc; conversion factors would then be expressed in ppm, zinc equivalent. Calibration of dithizone solution with zinc standards indicates that 1 ml of 0.001 pct dithizone is equivalent to approximately 0.25 ppm of zinc. An authoritative report on dithizone field tests authored by H. E. Hawkes in the June-July 1963 issue of Economic Geology* states "The appeal of these techniques has been the simplicity and speed of the determinations as compared with more tedious laboratory determinations of trace metals in weathered rocks, soils, or plant materials. This obvious appeal, however, has often been more than matched by misuse of the method in such a manner that the results are

Jan 1, 1964

By N. E. Grosvenor

The present and future activity of western coking coals is discussed. A general description of location, quantity, and quality is used as a basis for discussing development, mining, and marketing problems facing these reserves. As the need for coke from the West increases, solutions to the present mining and transportation problems will be forthcoming. Improved mining and blending technology, coupled with a more economical transportation solution, must precede a rapid development of the West's coke reserves. Ever increasing demands on coke production enhance the prospects of an accelerated development of these reserves.

Jan 1, 1976

By E. Escobar Pallares

Footnotes to column heads and explanation of symbols are given on page 239. H.C.T. means the deep zone for High Cold Test crude oil. L.C.T. means the shallow zone for Low Cold Test crude oil. They occur in the same area. In the same area there are many shallow pits and some wells. In the column showing total oil production to the end of 1939 are included 355,997 bbl. from shallow pits before 1939. During the last year there was no production from shallow pita.

Jan 1, 1940

By E. Escobar Pallares

Footnotes to column heads and explanation of symbols are given on page 239. H.C.T. means the deep zone for High Cold Test crude oil. L.C.T. means the shallow zone for Low Cold Test crude oil. They occur in the same area. In the same area there are many shallow pits and some wells. In the column showing total oil production to the end of 1939 are included 355,997 bbl. from shallow pits before 1939. During the last year there was no production from shallow pita.

Jan 1, 1940

By William B. Plank

For the first time in four years the number of mineral engineering students in the 228 engineering colleges of the U. S. and Canada exceeds 10,000. According to figures just released by the American Society for Engineering Education, the current enrollment of all engineering students is 222,178. The total of 10,274 mineral engineering students, undergraduate and graduate, is a 4% pct increase over a year ago. Total engineering is 11 pct larger than last year, about the same as in 1949-50, and 24 pct above 1950-51.

Jan 4, 1955