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The Library of the above-named Societies is open from 9 A.M. to 9 P.M. on all week-days, except holidays, from September 1 to June 30, and from 9 A.M. to 6 P.M. during July and August. The Library contains about 55,000 volumes, including sets of technical periodicals and the publications of scientific and technical societies. Members of the Institute, with few exceptions, are forced to spend a portion of their time in localities isolated from sources of information. To these the Library can render valuable service through correspondence; letters requesting information will receive special attention. The Library is prepared to furnish references and copies of articles on mining and metallurgical subjects; to determine the existence of mining-maps, and to furnish general information as to the geology and mineral resources of all countries. All communications should be made as definite as possible so that the information received may be what is desired and not include collateral matter which may not be of interest. The time spent in searching for such collateral matter will be saved, and the information will be sent more promptly and in more usable-shape. The members of the Institute can be of service to the Library by forwarding copies of mining-reports, maps privately issued, and similar material, which will be classified, indexed, and made available to other members. Suggestions for additions to the Library, either by purchase or personal solicitation as gifts, will be welcomed. It is hoped that members while in the city will use the Library freely, and assurance is given that most careful service will be rendered to them.

Jan 2, 1914

By Joseph E. Pogue

The writer visited the Muzo emerald mines in July, 1915, and spent six days in their study. This paper embodies the results of his observations, plus information personally communicated by Robert Scheibe, Professor of Geology in the Mining Academy of Berlin, who at the time of the visit was completing a detailed field investigation of nearly a year's duration of the emerald deposits of Colombia. An elaborate account of this valuable work may be expected at a future date from the pen of Professor Scheibe.

Jan 1, 1917

By S. Acar, P. Somasundaran

The results obtained for the selective flocculation of natural ores do not usually agree with the corresponding properties of the constituent minerals when present alone. This is mainly due to the presence of dissolved mineral species which can interact in many ways with other components in the system and alter their behavior. In this paper, the effect of dissolved species on the flocculation and electrokinetic properties of sulfide minerals is discussed. Dissolved iron, copper, and nickel (Fe, Cu, and Ni) species are found to affect the properties of natural chalcopyrite and pentlandite in certain pH range. These effects are interpreted in terms of species adsorption leading to activation or depression of reagents, surface precipitation, and complexation of species

Jan 1, 1986

By W. F. Stowasser

A downdraft traveling grate process to agglomerate pelletized iron ore concentrates has been successfully demonstrated in a pilot plant at Carrollville, Wis. Work there followed several years of development in the Allis-Chalmers Mfg. Co. laboratories, and the pilot plant phase was carried out in co-operation with Arthur G. McKee & Co., consultants and engineers to the iron and steel industry. End result of the process is conversion of iron ore concentrates into a form which can easily be transported and smelted in the blast furnace.

Jan 5, 1955

The volumes of Transactions, which are published annually, contain the list of officers, rules, etc., the Proceedings, and the papers revised for final publication. (In this revision, after the preliminary publication, authors are permitted to use the largest liberty; and the changes and additions made in papers are sometimes important. It should be borne in mind by those who study or quote a paper in the preliminary edition, that they may not have in that form the ultimate and deliberate expression of the author's views. It should be added, however, that in the majority of cases there are no important changes.) These volumes are for sale as follows, in paper covers:

Jan 1, 1917

By D. Watson, T. J. N. Grainger-Allan

A technique for studying the mechanism of the froth flotation process in which continuous froth removal does not take place but, instead, an equilibrium is reached between froth and pulp is described. A flotation cell, specially designed to facilitate equilibration, and froth and pulp sampling procedures are described. The main advantage of the technique is that the ability to measure the steady-state froth height allows froth-stability effects to be separated from pulp-process effects. In the flotation of hematite front quartz, linear relationships are found between airflow rate and froth height and between airflow rate and the ratio at equilibrium of mass of values in froth to mass of values in the pulp. A simple mechanistic interpretation of these results is given. It is suggested that froth-stability effects may play a more important role than hitherto allowed. In particular, the way in which concentration and size distribution of gangue particles may affect overall flotation rate is shown.

Jan 1, 1975

By H. I. Aaronson, H. A. Domian, G. M. Pound

Zener's two-parameter theory of the y a reaction in Fe-X alloys is extended to encornpass austenite-stabilizing as well as fewite-stabilizing elements, and is then cottzbitzed with statistical thermodynamic theories of Fe-C alloys to permit development of a ther-modynamic description of the proeutectoid fewite reaction in Fe-C-X alloys. Equilibrium tielines are calculated for tile a + y rep'on from experimental data and frort extrapolations of the y/y +a equilibrium surface. Sectzovs of the y/y + 0 surface are calculaled for the tzetastable sstuation LYL u-kich alloyrtg eleitzents do not partition betzseen azrstenite andfer-rite. The finding that the metastable y/a + y curves Lie close to their equilibriuwz counterparts when X = Si, .Vo, Co, Al, and Cu but well below them when X = A/ln or Ari pr-elides a thermodunamic explanation for the expcri1?7e?ztally obserted absence of partition during the proeutec toid ferrite reartlon in the fortner alloys and for the occurrence of partition at hzgher ternperatures in the latter alloys. Cotarison ofno- patitzoa free-energy changes and y/y i a curr,es in Fe-C-X alloys with the equilibrium 11al1es of these quantities in Fe-C alloys furnishes additional qualitative insight into the irqluence of allojling elements upon the kinetics of the proeutectoicl ferrite reaction. THE introduction of a substitutional alloying element, X, appreciably complicates calculation of the thermodynamics of the formation of proeutectoid ferrite from austenite. As noted in the preceding paper,' the positional entropy of the interstitial species is the principal component of the free energy of an interstitial solid solution with which theory has so far been able to deal. One would expect, however, that other components of the free energy of this type of solid solution may be significantly altered by the addition of a substitutional alloying element. Even if the assumptions are made, by analogy to the case of Fe-C alloys,' that changes in the positional entropy of carbon represent a significant part of the thermodynamic effects of an alloying element, and that the remaining effects can be taken into account by fitting the equations developed on this basis to experimental data on Fe-C-X phase diagrams or on the activities of carbon in alloyed austenite and ferrite, the experimental information available on either of these quantities is not yet sufficiently accurate or extensive, respectively, to make such an approach useful. An attempt made by Zener on the former basis to explain the effects of alloying elements on the thermodynamics of Fe-C alloys in terms of a temperature-independent "free-energy change" (actually enthalpy hane') required to transfer 1 mole of an alloying element from austenite to ferrite, in which the "free-energy change" was determined by fitting the theoretical relationships developed to Fe-C-X phase diagrams, thus proved inadequate in part because of deficiencies in the available ternary-phase-diagram data.= Other difficulties of a more fundamental nature, however, also indicated the desirability of a different approach to the problem.3y4y6 zener6 subsequently proposed that the free-energy change associated with y — a transformation in pure iron can be decomposed into magnetic and nonmagnetic components. Alloying elements were assumed to affect those components separately. One parameter was used to describe the quantitative effect exerted on each component. These parameters were evaluated from Ms (martensite-start) temperature data and from other experimental information usually either readily available or measurable with acceptable accuracy. Zener applied this treatment only to the calculation of Fe-X phase diagrams in which X is a ferrite-stabilizing element. In the present study, this treatment is extended to include austenite-stabilizing elements, and then combined with treatments previously considered for Fe-C alloys1 to permit calculation of the thermodynamic quantities of interest in the austenite - proeutectoid ferrite transformation in Fe-C-X alloys, where a number of representative, and commonly used alloying elements are chosen for X, including Si, Mn, Co, Mo, Al, Cr, and Cu. The results are used to explain important features of the partition of alloying elements between austenite and proeutectoid ferrite, as reported in a companion paper7 on the basis of electron-probe analysis, and to provide some additional understanding of the influence of alloying elements upon the kinetics of nucleation and growth of proeutectoid ferrite. Portions of this treatment6 have been clarified in the course of a review by Kaufman and Cohen.3 The consolidated summary of these developments with which this section is begun provides a basis for further clarification of the treatment, from which extension to include austenite- as well as ferrite-stabilizing elements is a natural consequence. The division of the free-energy change associated with the 7 - a transformation in pure iron, into two independent components is formally stated as:

Jan 1, 1967

By Robert S. Williams

On several occasions, when 60-40 brass is first obtained in the beta condition by quenching at about 825" C. and is then reheated, the writers have noticed that reerystallization will take place in the form of twin crystals at the grain boundaries of the original beta crystals. It was, therefore, thought that interesting results would be obtained if this twinning process was studied further, especially as to the temperature at which it first occurs. The material used in the investigation was a bar of extruded muntz metal, 1/2 in. in diameter, and of the following composition: Copper, 60.21 per cent.; zinc, 39.73 per cent.; lead, trace; iron, trace; tin, nil. Specimens 1 in. in length were sawed from this bar and a hole was drilled into the side of each specimen until it reached the center, and the tip of a platinum-platinum rhodium thermocouple was inserted. A small Hoskins' resistance-type electric furnace was used for heating the specimens. The specimens were first heated at 840' C. for 2 hr. and then quenched ' in cold water, in order to get the material entirely in the beta state. In every case, in the reheating process, the furnace was brought to the desired temperature before the specimen was introduced. The time occupied in preheating was from 20 to 30 min. By sawing back 1/4 in. on each side of the hole, two parts were obtained from each specimen and duplicate observations were possible. The specimens were held at the reheating temperatures for periods of 15 min., 30 min., 1, 2, and 4 hr. All specimens were etched with a freshly prepared mixture of equal volumes of concentrated NH4IOH and H2O2.

Jan 1, 1924

By R. V. Norris

In a former paper on this subject,' I summarized Murgue's theory and experiments, and presented a large number of tests of mine-fans, stating some conclusions, " more or less warranted by the evidence," as to design, capacity and efficiency. Since that time the very valuable report of Mr. M. Walton Brown: Committee on Mechanical Ventikators, Institution of Mining Engineers, has appeared, and I have made additional experiments which tend to clear up some points in connection with this subject. Design and Tests of the Luke-Fidlbr Colliery Fan. The Luke-Fidler fan (see Figs. 1, 2 and 3), built to replace an old wooden fan at a very fiery colliery, presents some pecu-

Jan 1, 1905

By R. E. Boni, G. Derge

SURFACE tensions of molten silicates are of metallurgical importance for many reasons. From a knowledge of their values, an insight into the problem of liquid slag structure can be gained. Also, such problems as separation of slag from metal, slag penetration of refractories, spreading of enamel coats on metals, bonding of cutting wheels, adsorption of gases, frothing of slags, and homogen-ization of slags are related to the surface tensions of the silicates. Because of the absence of a correlated review of the work that has been conducted in this field, the following survey is presented. It is not a complete summary of all the surface tension studies of silicates but only a review of the literature which is pertinent to metallurgical applications and research. Liquid Surface Tension The surface of a liquid differs from the interior in that its particles (ions, atoms, or molecules) are not

Jan 1, 1957

By D. D. Porter, H. G. Carlevato

Blasting to prepare orebodies for in situ leaching usually involves extraordinary conditions which sometimes require special and innovative techniques. To date several unusually large blasts have been made for leaching with results that are very encouraging. Among the factors considered when designing these large blasts are orebody shape and depth, rock properties, vibration and damage potential, loading logistics, and safety. All of these factors, and others, are discussed with an effort made to put each of them into its proper perspective.

Jan 1, 1974

By Archer E. Wheeler, Milo W. Krejci

The Boston & Montana Reduction Works at Great Falls, Mont., was formerly the reduction works of the Boston & Montana Consolidated Copper & Silver Mining Co., and continued as the reduction plant for the independent company until June 1, 1910, when the consolidation of a large number of the operating companies of Butte was effected. It then became merged in the Anaconda Copper Mining Co. as the Boston & Montana Reduction Department of the Anaconda Copper Mining Co. The history of copper converting at this plant, while not covering the entire period of the commercial use of the process in this country, does cover by far the larger part of it, and as the operation of and appliances for the process have undergone many changes during the time, it may, perhaps, be of some interest to put the record of these changes into permanent form. The plan followed in the preparation of this paper has been to give first a brief chronological record of the principal events and changes and then, even at the risk of some repetitions, to give more detaild accounts of some of these changes under separate headings. The headings for the complete paper are as follows: 1. General. Chronological Review. 10. Development of Different Classes 2. Mechanical Manipulation. of Converters After Class I. 3. Casting of Finished Copper. 11. Basic Lining. 4. Tamping of Linings. 12. Number and Size of Tuyeres. 5. Early Acid Linings. 13. Cast Copper Tuyeres. 6. Acid Linings With the Use of Ore. 14. Efficiency of Air. 7. Introduction of Flux Through the 15. Size of Converter Mouth. Tuyeres. 16. Height of Converter. 8. Bottom Blast. 17. Summary. 9. Disposal of Converter Slag, General Chronological Review. Ground was broken for the general concentrating and smelting plant in the spring of 1,891. The first departments to start operations were the concentrator in March, 1892, and the Brückner roasting and reverbera-tory smelting departments in April, 1892. The converter department

Jan 1, 1914

By Robert G. Van Nostrand, John H. Henkel

TRANSIENT potentials obtained in resistivity prospecting can be separated into two classes. The first is electromagnetic, has a comparatively short time constant, and increases in relative amplitude as the electrode separation is increased. These electromagnetic transient potentials, of which an excellent theoretical treatment is given by Yost: are the result of changes in the current and can be classed as differentiated signals. The second class is electrochemical, has a comparatively long time constant, and decreases in relative amplitude as the electrode separation is increased. The electrochemical signals are generated by the current flow itself and can be classed as integrated signals. The transient potentials due to electrochemical factors are the subject of this article. The phenomenon is referred to as induced polarization. Schlumberger" was the first worker to observe induced polarization, but he was unsuccessful in attempts to apply the principles of induced polarization in electrochemical prospecting. Other workers, notably Bleil; have studied polarization and in some cases pointed out its possibilities, but no theory has been presented that describes polarization and its time dependence adequately. It is the purpose of this discussion to present the essence of a theory to geo-physicists and to show that it leads to results consistent with experimental evidence. The theory on which this analysis is based has existed in electrochemical circles since 1910."

Jan 1, 1958

By Eugene Guccione

Before answering the question raised in the title, let's briefly consider how East-West trade is viewed within the entire US political spectrum. Essentially, there are four major schools of thought: (1) The Peaceful-Coexistence School. Advocates of this school call themselves free-traders and hold to the premise that: (a) trade benefits all parties involved, hence it is the best tool to achieve peace; (b) US trade barriers should be removed, and the quicker the better; and (c) negotiations, cultural exchanges, and political compromise should be used extensively.

Jan 9, 1974

By J. N. Maycock, P. W. M. Jacobs

Previous measurements of the thermoelectric power of ionic crystals are reviewed briefly. It is concluded that, while extensive measurerements are available on systems in which the electrode M has a cation in cornon with the sall MX, there is as yet little modern work on systems in which the metal electrode M' does not haue a calion in common with the salt. We haue now measured the thermoelectric power of- single cryslals of KC1 and of KC1 + SrCl2 between plati.nu?n electrodes over a much wider range of temperature than before. individual ionic heats of transport, which, while probably not very accurate, are of a reasonable order of magnitude, are obtained from this data on the basis of an assumption that charge carriers do not cross the electrode/salt interface. RELATIVELY little work has been done on thermal diffusion in ionic crystals. Reinhold and coworkers1-I measured the thermoelectric power and Soret effect in silver and cuprous salts and their mixed crystals. One electrode was kept at constant temperature and electromotive force was measured as a function of the temperature gradient. This is not a satisfactory technique if the results are to be compared with theory; rather should the electromotive force be measured for small temperature differences as a function of the mean temperature of the two electrodes. They used electrodes having the same cation as the salt. Patrick and Lawsons measured the thermoelectric power of AgBr and of AgBr containing 0.25 mole pct CdBr2 using silver electrodes and temperature gradients of 10°C in the temperature range 100° to 400°C. The results were analyzed using the Teltow9 values of the ratio of the mobility of the two types of charge carrier (cation vacancies and interstitials) found from conductance measurements and the wagnerlo estimate of the heterogeneous contribution to the thermopower, Ohet They obtained values of qi = 0.017 ev and q$ = -0.385 ev for the heats of transport of interstitial Ag ions and cation vacancies, respectively. Their data has been reanalyzed by Haga using the corrections to the Wagner formula for ehet given by Howard andLidiard; Haga found ev. Christy et a1.14 have measured the thermopower of AgBr containing 0.01 to 1.0 mole pct CdBr,. They analyzed their results in terms of the theory of Howard and Lidiard and found that excellent agreement with the theory was obtained if q5 + : + hF was set equal to 0.70 ev at 175°C and equal to 0.58 ev at 250°C. Since Teltow's value for hF, the enthalpy of formation of a Frenkel defect pair, is 1.27 ev, this means that qt + q: increases in magnitude from -0.57 ev at 175°C to -0.69 ev at 250°C. This result is in poor agreement with Patrick and Lawson's value of -0.37 ev for pure AgBr (for which the corrections to the Wagner estimate for ehet are very small). christy1' has also reported thermopower measurements for pure silver halides and for the systems he finds that qr + qt for AgBr increases in magnitude from about -0.55 ev at 150°C to about -1.1 ev at 400°C. The temperature dependence of the sum of the heats of transport in AgCl is very similar in magnitude. The sum qi + q cannot be decomposed into the individual interstitial and vacancy heats of transport without a knowledge of the entropy contribution from the change in the lattice vibrational frequencies around the interstitial and vacancy. Despite this it seems an inescapable conclusion from Christy's analysis that and -6 = Q Ag are quite strongly temperature-de pendent and that -q: is much greater in magnitude than the corresponding activation energy for vacancy migration, +0.37 ev. It remains a mystery as to why the data for pure AgBr are fitted so well by the assumption of temperature-independent heats of transport if association of impurity ions and vacancies is neglected.l The values for q$ and q: so obtained are also much more in line with those expected from a simple kinetic interpretation of the heats of transport due to wirtz.17 Christy and Hsueh have also measured the thermopower of CuCl between copper electrodes; 0 for pure CuCl is comparable with that for the silver halides but, owing to the limited solubility of divalent cation impurities it was not found possible to deduce values for the heats of transport. In contrast to these extensive measurements on cells of the type M MX 1 M, there have been relatively few attempts to measure the thermoelectric power of cells of the form M' 1 MX I M'. (We specifically exclude from discussion cells of this type in which the metal electrodes M' are in contact with gas containing a controlled partial pressure of either M or X,, since in these cells the electrochemical reactions are analogous to those of the first type.) The thermoelectric power of Pb12, PbC12, TlC1, TlBr, TlI, NaNO3, and KNO 3 between platinum electrodes was measured by Thie1e.l3 In discussing these measurements Holtan20 asserts that the thermopotential initially fluctuated wildly and even changed sign before approaching a steady value. A high degree of irreproducibility is also evident in the work of Nikitinskaya and Murin21 who first studied the thermopower of NaCl and KC1 between platinum electrodes. Much better reproduci-bility was achieved in our earlier measurements on KC1;22 these were, however, confined to a relatively narrow temperature range and one of the objects of the work reported in this paper was to extend the temperature range of the measurements of the thermoelectric power 8 of KC1. The only other published

Jan 1, 1967

By J. H. Smith, H. W. Paxton

X HE recent investigation of Butler, McCabe, and paxton' on the vapor pressure of manganese gas in equilibrium with Mn-Fe alloys has been extended to include the iron-rich solutions and alloys in the two phase equilibrium region. The study of the phase equilibrium by Kurnakov and Troneva2 and the extensive reviews of the Mn-Fe system by Hansen,3 and Hellawe114 are not in agreement with regard to the location and extent of the equilibrium between the solid phases of fcc y and complex P in the temperature range above the eutectoid temperature of approximately 975Kwhere 0 decomposes to y and bcc a. An evaluation of the existing equilibrium data is confronted with the conflicting results presented by various investigators who used techniques requiring a quenching treatment to retain the high-temperature equilibrium or encountered temperature hysteresis during thermal analyses. The difficulty of suppressing the transformation of the manganese-rich concentrations of the y-solid solution during quenching has been well etablished.' To avoid this uncertainty the phase equilibrium was investigated at temperature by measuring the partial pressure of manganese gas in equilibrium

Jan 1, 1962

By H. E. Rorschach

Activity in Oklahoma fields declined in 1938 from the banner year of 1937. During the year, 1768 wells were completed as compared to 2632 completed during the year 1937. The following tabulation sets out details regarding the wells completed during the year: These computations do not take into account the wells drilled for repres-sure and salt-water disposal, and other nonexploratory wells. Purchasers' reports filed with the Corporation Commission of the State of Oklahoma show a total of 168,789,229 bbl. of oil purchased from Oklahoma leases in 1938, or a daily average of 462,436, a decrease of about 25 per cent from the year 1937. The outstanding operation of the year was the further development of the Ramsey pool, in western Payne County, the producing horizon being classified as the Wilcox. This pool was discovered on the last day in the year 1937, by the Mid-Continent Petroleum Corporation drilling on a unitized block in see. 18, T. 18 N., R. 2 E. The map in Fig. 1 shows the development at the end of the year 1938. An important discovery of the year was the Champlin Refining Company's No. 1 Boehm, in Garfield County, sec. 4-24N-8W., the producing horizon being the second Wilcox found at a depth of approximately 6700 ft. This pool was assigned the name of Hillsdale. Some of the offsets to this discovery well had not come up to expectations at the end of the year, but the discovery seems to be important as indicating that the Wilcox sand is productive in the Anadarko Basin area, providing that the right structural conditions are present.

Jan 1, 1939

By H. E. Rorschach

Activity in Oklahoma fields declined in 1938 from the banner year of 1937. During the year, 1768 wells were completed as compared to 2632 completed during the year 1937. The following tabulation sets out details regarding the wells completed during the year: These computations do not take into account the wells drilled for repres-sure and salt-water disposal, and other nonexploratory wells. Purchasers' reports filed with the Corporation Commission of the State of Oklahoma show a total of 168,789,229 bbl. of oil purchased from Oklahoma leases in 1938, or a daily average of 462,436, a decrease of about 25 per cent from the year 1937. The outstanding operation of the year was the further development of the Ramsey pool, in western Payne County, the producing horizon being classified as the Wilcox. This pool was discovered on the last day in the year 1937, by the Mid-Continent Petroleum Corporation drilling on a unitized block in see. 18, T. 18 N., R. 2 E. The map in Fig. 1 shows the development at the end of the year 1938. An important discovery of the year was the Champlin Refining Company's No. 1 Boehm, in Garfield County, sec. 4-24N-8W., the producing horizon being the second Wilcox found at a depth of approximately 6700 ft. This pool was assigned the name of Hillsdale. Some of the offsets to this discovery well had not come up to expectations at the end of the year, but the discovery seems to be important as indicating that the Wilcox sand is productive in the Anadarko Basin area, providing that the right structural conditions are present.

Jan 1, 1939

By G. Pizzi, G. M. Ciucci, G. L. Chierici

The use of the material balance equation to estimate the volume of hydrocarbons originally present in a reservoir, whose producing mechanism is partly due to water drive, has been discussed in the literature by several authors. There is no general agreement upon the possibility of obtaining reliable results by this method. Gas reservoirs in contact with an active aquifer are considered in this paper. Theoretical considerations based on the cybernetic principle of uncertainty (which states that the internal structure of a system cannot be uniquely determined from its observed external behavior) lead to the conclusion that the volume of gas originally present in a reservoir of this type cannot be uniquely determined from its past history. The range of values which encompasses the actual value of the reserves varies from case to case and must be determined by either numerical or analogical methods. Results obtained for six gas fields are reported. All these fields were produced with small fluctuations in their production rates, as is common practice for gas reservoirs; no gas storage fields were considered. Results obtained show that reserves values in a range of 1 to 2, associated with appropriate aquifers, allow the matching of the reservoir past history with mean-square deviations less than the experimental errors involved in pressure and produclion measurements. Similar results have been found in several other partial water drive gas reservoirs. From these results it is concluded that gas reserves cannot be uniquely determined from the past performance of partial water drive reservoirs, at least in cases where the reservoir has been submitted to small fluctuations in the production rates, and pressure data of normal accuracy are available. INTRODUCTION A number of authors have analyzed the problem of estimating the reserves originally present in a partial water drive reservoir from its past pressure-production performance. Literature which deals with this subject can be grouped, according to their conclusions, as follows. 1. A reliable value for the reserves can be obtained even if reservoir data (pressure and cumulative production) are affected by errors within the normal range.'-' 2. A reliable value for the reserves can be obtained only if reservoir data are very accurate'- or if past production performance has been subjected to abrupt variations in the production rate."' 3. No unique value for the reserves can be obtained from reservoir past production performance. This conclusion has been based upon theoretical considerations" and verified in several field cases. The purpose of this paper, which deals only with partial water drive gas reservoirs, is to test the above conclusions against actual field cases. Some theoretical considerations on this problem are also presented. THEORETICAL CONSIDERATIONS As the behavior of a gas reservoir communicating with an aquifer depends on both the aquifer and the reservoir characteristics, the physical system to be studied is the combined gas reservoir plus aquifer. The information which is available for studying the performance of such a system is the well production rates and bottom-hole pressures, all given as functions of time. The external behavior of the reservoir-aquifer system is therefore described by 2n input variables (Gp, Wp,) and n output variables (p,), n being the number of wells in the reservoir. In reservoir engineering it is common practice to consider the reservoir as a whole, disregarding the internal distribution of pressures and of producing wells. This practice is equivalent to substituting the above multi-variable system with a single-variable system, where the average reservoir pressure is the only output variable and the cumulative production G,(t) and W,(t) are the input variables. The internal structure of such a system, defined by initial gas reserves G, aquifer shape and dimensions, boundary conditions and petrophysical parameters distribution throughout the aquifer, is unknown. Therefore, from a cybernetic point of view the system is a "black-box It has been demonstrated" that for a blackbox the indetermination principle holds. Accordingly, the number of different internal structures (or set of parameters) which can account for the observed external behavior is infinite. As a consequence, the initial reserves cannot be uniquely determined from the reservoir past performance. When W,(t) is known, the determination of G from

By J. J. Van Nouhuys

THE economics of aerial survey and the technical processes by the aid of which vertical and oblique aerial photographs are turned into line maps showing the most profuse topographical detail such as contours, rivers, roads, plantations, habitations and cultivated lands do not concern us here. They have been ably and exhaustively described in the publications of the British War Office, handbooks on surveying methods and on photogrammetry and in the South African mining, engineering and geological press. Suffice it to mention that for geological interpretation vertical photographs are used on such scales as 1/5000 to 1/10,000, overlapping each other by 55 to 60 per cent in the direction of flight and some 10 to 20 per cent sideways on to the next sequence or strip. Through this duplication in the overlap the stereoscopic examination becomes possible. The standards by which monochrome aerial photographs are interpreted can be grouped under the following headings: 1. Continuity.-The continuity of topographic relief not obtainable on the ground owing to the smallness of man relative to that relief. Here lies the greatest value of aerial survey with relation to geology. An immediate alignment can often be made of drainages running in different directions on each side of a hill; saddles and gorges in the mountainsides; abrupt termination of outcrop or indubitable signs of faulting. Most conclusive evidence is thus often obtained about faults which may be perfectly visible at one place on the ground but cannot elsewhere be identified because of decreased throw. Similarly, dikes can often be followed notwithstanding frequent interruption and disappearance under the soil. Scattered outcrop in scrub-covered or bush-covered country can be compared with field work. The same applies to geological contacts. Once these have been 3stablished at a few points on the ground, the intervening stretches can be drawn in.

Jan 1, 1937