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By Arthur Zentner

THE essentials of the electrolytic zinc process, as now used in commercial plants, date back to work done by Letrange in 1881. He used sulfuric acid to leach roasted sulfide and ,oxide ores, purified his solution very much as we do now, and electrolyzed the purified zinc sulfate solution. Ten years later Hoepfner developed a process using chloride solutions, and built three plants. One in England operated until 1924 in one of the works now merged in the Imperial Chemical , Industries, Ltd. Ashcroft built a plant in 1898 in the Broken Hill district of Australia. He used both chloride and sulfate solutions.. While his work failed, the aid his published results have been to later workers has made him an outstanding contributor to the de- velopment of the electrolytic zinc process. A good deal of work was done in the following years, aiming to electrolyze zinc chloride solutions and fused zinc chloride. Quite a bit of work on sulfate solutions was also done in the last years before the war. With the outbreak of the war, metal demand and rise in metal prices provided the stimulus which resulted in the remarkably rapid commercial development of electrolytic zinc. In this last period of development, all the work brought to commercial fruition has been with sulfate solutions. The high-density process, or the Tainton process, is used, as you know, in the Sullivan electrolytic zinc plant at Kellogg, Idaho, and will be used in the Evans- Wallower plant now being built at East St. Louis. The low-density process is used by the other plants now operating in the United States and other countries. There are now in operation and under construction four electrolytic zinc plants in the United States, two in Canada, two in Italy and one each in Australia, Rhodesia, Poland, Norway and Germany.

Jan 1, 1929

By M. J. Sinnott

WITH the advent of nodular iron as an engineering material, considerable interest has been shown in developing this material for various applications. Generally the strength, hardness, or ductility are the more common properties used for design purposes but occasionally applications involving a knowledge of the thermal conductivity of the material is required. A search of the literature showed, rather surprisingly, that relatively little work has been done on this property for all types of cast iron. Insufficient data are available on thermal and electrical conductivities to develop the Weidemann-Franz ratio, or the Lorentz relationship, for estimation purposes. There are no data on nodular irons and the published data on malleable irons are quite sketchy. For these reasons the conductivity of the group of nodular irons listed in Table I were measured. Irons I to IV were made in such a fashion as to maintain the carbon and alloy content essentially the same while varying the silicon content. Test specimens were cut from the mid-section of 4-in. keel castings. Iron V is a commercial casting of nodular iron. The test specimen of this iron was cut from the center of a large cast billet 3x10x26 in. All alloys were tested in the as-cast condition. A microstructural examination showed that each iron had spheroidal graphite but the size and distribution varied with the silicon content of the iron. The spheroid size decreased while the number of graphite nodules increased as the silicon content of the iron was increased. The matrix structures of each iron consisted of pearlite and ferrite with the proportions varying from predominantly pearlite in the low-silicon iron to mostly ferrite in the high-silicon iron. The commercial heat, iron V, was predominantly pearlite probably because of its higher manganese and phosphorus content. Two methods for measuring the thermal conductivity were used. The first was a modification of the techniques described by Powell and Hickman and Van Dusen and Shelton,² the second method was a simpler technique described by Jakob and Hawkins." Since the agreement of both methods as tested on two sets of duplicate samples was excellent, the simpler experimental technique was used. The results of the measurements are given in Table II along with a summary of the microstructural constituents. These conductivity data indicate that as the percentage of silicon increases there is a corresponding decrease in the thermal conductivity even though the structure is changing from pearlitic to ferritic. Such a change in microstructure is usually accompanied by an increase in conductivity. A third factor involved in the behavior of these irons is the size and distribution of the graphite nodules. The relative amounts of graphite do not change greatly but the size and distribution do. Generally graphite improves the conductivity but in the present case such an effect is probably masked by the alloying effect from the silicon and its dispersion through the matrix. The thermal conductivity of the nodular irons studied is less than that of regular foundry irons by some 10 to 30 pct and is less than that of regular malleable irons.' The cause of the decreased conductivity is probably the more highly alloyed fer-rites obtained in these irons and the changed mode of distribution of the graphite as compared to the regular foundry irons. References R. W. Powell and M. J. Hickman: Journal Iron and Steel Inst. (1946) 154, No. 2, p. 99. 'M. S. Van Dusen and S. M. Shelton: U. S. Bur. Standards Journal of Research, RP668 (1934) 12, p. 429. ³M. Jakob and G. A. Hawkins: Elements of Heat Transfer and Insulation. 2nd Ed. (1950) New York. John Wiley and Sons. ' J. W. Donaldson: Journal Iron and Steel Inst. (1933) 128, No. 2, p. 255.

Jan 1, 1954

By Sam Tour

WHAT is a die-casting and what is the die-casting industry? From the literal translation of the words "die" and "casting"' one concludes that a die-casting is a casting made in a die. The casting may be of any metal or alloy or, for that matter, may be of some nonmetallic material capable of being cast, such as plaster of paris or glass. The die may be of any material that will take successive casts so it need not necessarily be metallic in nature. The term "die-casting," therefore, is indeed broad, though in practical usage it has come to mean the casting of metals and their alloys in metallic molds or dies. Even this limitation of the term leaves -a broad field, for castings may be made in a number of different ways. For example, the molten metal may be allowed to run into the die by gravity it may be sucked into the cavity of the die, it may be forced to take the contour of the cavity in the die by centrifiugal force, or it may be forced into the cavity under hydrostatic pressure. In England, castings made by practically all of these

Jan 1, 1935

By Frank S. Gardner, Morris Cohen, Dara P. Anita

There is a conspicuous lack of information in the literature on the precise role played by residual quantities of austenite in heat-treated steels. While retained austenite may be expected to have significant effects on such important properties as the impact resistance of tools and carburized parts and the dimensional stability of dies and gauges, attempts to study these problems systematically have suffered from the absence of a reliable technique for ascertaining absolute amounts of austenite. With such a technique, not only could the relation between residual austenite and service behavior be investigated, but the chemical and heat-treatment factors that control the quantity of the austenite could also be established. Thus, the retained austenite content could then be regulated in accordance with the results desired. The presence of retained austenite may be inferred by observing the changes in properties (hardness, specific volume, electrical resistance, etc.) due to its decomposition on subatmospheric cooling1 or on tempering,2 but these indirect measurements are not readily translated into percentages of austenite. Quantitative determinations have been achieved in special cases by means of dilatometric3 and magnetic4,5 measurements; but the former procedure requires that observations be conducted during the hardening and involves difficult calibrations that limit its applicability, while the magnetic procedure is very sensitive to extraneous influences and depends upon assumptions that can only be considered as approximate in an absolute sense. Furthermore, both the dilatometric and magnetic effects are volume properties, and cannot be conveniently utilized to explore variations in retained austenite from point to point in a suecimen. Some microstructures lend themselves to accurate evaluation of retained austenite contents by metallo-graphic methods,3 but such instances are not too common, and at best, the procedure is tedious. The characteristic X-ray diffraction lines of austenite permit positive identification of its presence; and in the present paper the intensities of these lines, or the corresponding densities* on photographic film, are employed to measure the amount of the retained austenite. In order to cancel the effect of uncontrollable variations in the X - ray exposure and film - development conditions, a standard reference line is Superimposed on each film by maintaining a foil of aluminum in the path of the incident X-ray beam during the entire exposure. With different samples of steel and the same foil, the ratio of the density of some one austenite line to the density of

Jan 1, 1943

By Morris Cohen, Dara P. Anita, Frank S. Gardner

There is a conspicuous lack of information in the literature on the precise role played by residual quantities of austenite in heat-treated steels. While retained austenite may be expected to have significant effects on such important properties as the impact resistance of tools and carburized parts and the dimensional stability of dies and gauges, attempts to study these problems systematically have suffered from the absence of a reliable technique for ascertaining absolute amounts of austenite. With such a technique, not only could the relation between residual austenite and service behavior be investigated, but the chemical and heat-treatment factors that control the quantity of the austenite could also be established. Thus, the retained austenite content could then be regulated in accordance with the results desired. The presence of retained austenite may be inferred by observing the changes in properties (hardness, specific volume, electrical resistance, etc.) due to its decomposition on subatmospheric cooling1 or on tempering,2 but these indirect measurements are not readily translated into percentages of austenite. Quantitative determinations have been achieved in special cases by means of dilatometric3 and magnetic4,5 measurements; but the former procedure requires that observations be conducted during the hardening and involves difficult calibrations that limit its applicability, while the magnetic procedure is very sensitive to extraneous influences and depends upon assumptions that can only be considered as approximate in an absolute sense. Furthermore, both the dilatometric and magnetic effects are volume properties, and cannot be conveniently utilized to explore variations in retained austenite from point to point in a suecimen. Some microstructures lend themselves to accurate evaluation of retained austenite contents by metallo-graphic methods,3 but such instances are not too common, and at best, the procedure is tedious. The characteristic X-ray diffraction lines of austenite permit positive identification of its presence; and in the present paper the intensities of these lines, or the corresponding densities* on photographic film, are employed to measure the amount of the retained austenite. In order to cancel the effect of uncontrollable variations in the X - ray exposure and film - development conditions, a standard reference line is Superimposed on each film by maintaining a foil of aluminum in the path of the incident X-ray beam during the entire exposure. With different samples of steel and the same foil, the ratio of the density of some one austenite line to the density of

Jan 1, 1943

By R. W. Jenkins, O. J. Neslage

The need for mechanized drilling to decrease mining costs has resulted in the development of the jumbo from column-and-bar drill carriages to hydraulically controlled jib jumbos. Resultant savings from use of improved jumbos have been high enough usually to retire the machinery investment within a year. The jib jumbo unit has been applied successfully to development and preparation programs and flat-bedded stopes, and an even wider field is forecast for its use.

Jan 1, 1950

By G. A. Vissac

MOISTURE in coal must be considered as an impurity, just the same as ash, from the standpoint of utilization of the coal. Being incombustible, it reduces directly the heating value of the coal, and in addition absorbs heat for its evaporation. Its presence means useless expenditures in handling and transportation. In coke plants, extra moisture reduces capacity and may cause damage to brick work and equipment. Accordingly, the removal of extra moisture can be considered just as important as the removal of other impurities, such as ashes, in the modern coal preparation plant. Moisture, which can be removed by heating the coal up to a temperature of 100°C, may be retained in various forms: 1. As a film, on the surface of each coal particle, and in the interstices between particles, retained by capillary forces. 2. Or "occluded" inside the coal particles. This occluded moisture may be either free moisture (as in a sponge), or hygroscopic moisture which varies with atmospheric conditions, (also called "regain").

Jan 1, 1949

By James R. Finlay

SOMETIMES the American Institute of Mining and Metallurgical Engineers appears to be a strictly technical society, and if so my paper should deal with the technical operations of finding and producing gold. But I have not been engaged in practical gold mining since 1910. What I have been doing mainly for the last 25 years is to try to figure out what the income of a mine-gold, or any other-would be worth to an investor. So I have been in contact with gold mining, in one way or another, for some 42 years. I say that with a purpose. In that time the industry has been through one of its cycles. The value of gold mines is very dif¬ferent at different points in one of these cycles. For this reason the cycle of gold mining is a highly practical study. The cycle of gold is a more or less rhythmical change in its value or purchasing power measured in the grand average of other commodities, which is the same thing as its price. Taking the price of gold in 1897 as a stand¬ard, a dollar at that time declined to 55c. in 1913, to 26.8c. in 1920, and since then it has risen to 47.4c. in 1930 and to about 64c. in 1932. It is worth about 21/ times as much now as it was in 1920, but less than two¬thirds as much as in 1897. When this change is applied to the value of a gold mine still greater differences are evident. The cost of producing gold is of course measured in labor and other commodities, and as that cost goes down the margin of profit measured in the gold itself increases. Thus a mine which might make only 10 per cent profit in 1920 on its gross output may easily make 25 per cent now. The stockholder gets 2 ½ times more gold that is worth 2 1/2 times as much in purchasing power, therefore the real value of his holding has risen by the one factor multiplied by the other, giving him 61/4 times as much goods or services as he had in 1920.

Jan 1, 1933

By T. W. Guy

IN approaching the problems of sampling coal, a brief statement of certain facts that are more or less taken for granted may be helpful: 1. The coal-mine operator needs reliable data as to the physical and chemical characteristics of his coal in order to plan and control intelligently its mining, preparation, and marketing. The consumer needs such data in order to select the equipment and the coal best suited to meet his requirements, to check the quality of fuel delivered, and the efficiency of its use. Various government control agencies require such data as a basis for classifications and establishment of limits, for use in carrying out the requirements of federal, state or municipal laws. 91. All such data must be obtained by analyses, measurements, or tests made on samples, which are taken to represent the coal tested. It is now becoming generally recognized that, in accordance with statistical laws, test results from samples are not expected to represent the exact qualities of the lot or lots from which they are taken, except within statistical, or "expected limits. Such limits are definitely specified by some present standards of the American Society for Testing Materials and the British Standards Institution. 3. Samples that give ash within satisfactory limits are usually assumed to be sufficiently accurate for other analyses, except under special condi¬tions such as meeting close specifications for coals showing wide variability in sulphur, fusibility of ash, or other quality. 4. In modern coal sampling the increment is recognized as the basis for taking samples. For a given accuracy the number and weight of increments specified are increased with: (a) the expected ash, and (b) the top size designation of the lot to be sampled. 5. It is extremely important that every sampler recognize that: the specified number and weight of increments are minimums, and that the precautions to be used in order to take them properly are also minimums; that in the reduction of the gross sample the sizes specified for the coal after each stage of the crushing are maximum; that the quantities specified to be taken after each crushing stage are minimum; that any short cuts or failures to meet the requirements specified will reduce the statistical accuracy of the results, although it is possible that one or two checks on a few results may seem to show otherwise.

Jan 1, 1943

By A. J. Williams

THE province of Saskatchewan, situated in the center of the Great Plains region of Canada, has, like most prairie areas, an essentially agricultural economy. Most of its population of about 860,000 is located in the southern half of the province in the farming and ranching areas. To the north of the prairie is a broad forested belt supporting a considerable timbering industry, and the northern one third of the province is glaciated pre-Cambrian rock formation. This latter area is relatively barren of vegetation, but the presence within it of a considerable variety of radioactive, noble and base metals, and industrial minerals has been shown by prospecting in recent years.' Glacial Geology The Keewatin ice sheet, considered to have accumulated in the country to the west of Hudson Bay in Pleistocene time, covered at its maximum advancement almost all of Saskatchewan and extended south of the international boundary. Only in the Cypress Hills in the southwest and around Wood Mountain in the south central portion of the province did the preglacial formations escape the action for this glacial period. The bedrock of the plains and forest areas therefore is overlain by moraines and modified glacial drift, which vary in thickness from a few feet to 400 or 500 ft.' Glacial action in the pre-Cambrian area of the province was largely erosional, most of the more recent formations and some of the pre-Cambrian rock being transported out of the area to the south and west. It has been estimated that about 13 pct of this area is composed of lakes and rivers not too adaptable to rail or water transportation, so that until the use of aviation for exploration purposes became general, development of the area was slow. To the south, the heavy mantle of glacial drift has to some extent deterred the discovery of industrial minerals in the bedrock underlying the forest and prairie regions3 At the same time, this drift contains numerous deposits of those most elementary and necessary industrial minerals, sand and gravel. Sedimentary Basin The major feature of the sedimentary deposits underlying the plains regions is the basinal structure known as the Moose Jaw syncline, which runs from the southeast corner of the province in a northwesterly direction. To the west of this syncline the formations curve upward, then have been faulted and further upthrust to appear at the surface in the foothills of the Rockies in Alberta; to the east and north they curve upward into Manitoba and northern Saskatchewan, but the surface contacts are covered mostly with glacial drift.238 The axis of the syncline dips to the southeast, so that there is also an upward trend of the formations along the axis to the northwest. In illustration of the regional structure underlying the province, the pre-Cambrian basement has been logged in drillholes at the following depths in several locations: Ogema (south central), 9390 ft; Gronlid (northeast), 2599 ft; Vera (northwest), 4422 ft; Big River (north northwest), 2348 ft. Fig. 1 indicates the general surface geology of the province, ignoring such glacial overburden as may overlie many of the bedrock formations. Also indicated is the approximate location of the axis of the Moose Jaw syncline.' Industrial Minerals Clays: The province is fortunate in possessing a widespread distribution of clays of ceramic value, ranging from those used for heavy structural products to the high grade pottery and china clays. Shales suitable for brick and tile production are found in the Upper Cretaceous and Tertiary formations across the south of the province where the glacial drift is thin or nonexistent. Many deposits of glacial lake clays suitable for such wares are found scattered over the rest of the province south of the pre-Cambrian area. The Whitemud formation of the Upper Cretaceous is a narrow sedimentary band of secondary clays found intermittently at points across the south of the province where glacial action did not disturb or remove them.' In the southwest corner of the province, around Eastend in the Frenchman River valley, the refractory clays of this formation are contaminated somewhat with iron compounds or other alteration products of basaltic rocks. This eliminates the use of those clays in true whitewares, as they fire to creamy buff shades at the lower temperatures and to a blue-specked grey at cone 8 to 12, (2280°F to 2390°F), the range commonly used in firing whiteware. However, for use in the production of colored artware, caneware, stoneware or crockery, and sewerpipe, this type of clay makes an excellent body that requires little or no addition of flint, feldspar, or other fluxing materials such as are required in the higher class of ware.' It is not a grade of clay that can be shipped great distances to the manufacturing centers, but a market for considerable tonnages has developed at nearby Medicine Hat, where cheap natural gas is available for the firing of the ware. Farther east in the south central portion of the province, the clays of the Whitemud formation are generally more refractory and white burning. The formation is divided into three zones, consisting of white clays, brown shale, and white sandy clays.

Jan 1, 1953

By Ballard H. Clemmons

THE future of the steelmaking industry of the Birmingham, Ala., district is closely related to and, in a large measure, dependent on the development of workable, economic processes of ore concentration. Operations thus far in the area have been possible only because of the fortuitous occurrence of iron ore, fluxing stone, and coking coal-all the primary iron-making materials- within a 25-mile radius of the blast furnaces. Commercial ore of the district consists mainly of a 10 to 20-ft hematite-calcite-silica bed locally known as the "Big Seam," a component of the Clinton formation of Silurian Age. At present mining rates, this ore will be available for a number of years. It is largely mined under 1000 to 2000 ft of cover and transported on 15 to 20" slopes that, in some instances, are as much as 10,000 ft long. Under these conditions, particularly with increasing distances from face to portal, mining costs are gradually becoming disproportionately high. Although not a major factor thus far, it should also be noted that the average annual ore output of the district is gradually be- coming more siliceous.

Jan 1, 1950

By D. M. Wyslouzil

Standard testing methods are described that are presently used for the selection of grinding equipment. Correlation between laboratory batch grinding tests and pilot plant continuous tests are established by means of particle size distributions and flotation results. Conventional and autogenous grinding circuits are discussed showing the relationships of the controllable circuit parameters.

Jan 1, 1982

By I. A. Ettlinger

DEPRECIATION allowances have become firmly rooted in our income tax structure both by legislation and by court decisions. Secretary of the Treasury Morgenthau has recently stated before the Ways and Means Committee of the House: A taxpayer who did not provide for depreciation of assets used in his business could not long remain in business and the income tax should be levied on the assumption that he will provide for such depreciation. The 1934 Revenue Act has now been enacted, the depreciation provisions of the 1932 Revenue Act having been carried forward without change. However, there has arisen, in connection with the preparation of this new Revenue Act, a determination by the Treasury Department to make certain changes in the future administration of the depreciation allowances that will affect all corporations, and mining companies in particular.

Jan 1, 1934

By Walter Wood

The specifications for locomotive-cylinders, which are given in a separate paper at this meeting, have been prepared so that castings (upon the successful use of which so much depends) shall be made to conform to standards that will yield good results. After the essentials, which go with a sound and perfect cauting, the requirements to be borne in mind are those concerning the quality of the material. These have been determined from the actual practice of the largest users,—representatives of the American Locomotive Company, the Baldwin shops, and the Pennsylvania Railroad being upon the Committee. The results called for by the test-bar have been carefully checked by actual experiment upon metal that has given satisfactory service in cylinders.

Jan 1, 1905

By F. R. Milliken

EXPERIMENTS, in what has come to be known as flash roasting began some ten years ago. The principle underlying the operation was not a new one, but the experimental work started at that time was the first that was carried through to a logical conclusion, followed by construction and operation of a pilot plant, and then full-scale production. For a short working definition, flash roasting may he considered the instantaneous and complete oxidation of finely ground sulphide particles, partially suspended in air or gas, the oxidation reaction evolving enough heat to make the reaction self-sustaining, or nearly so.

Jan 1, 1937

THERE are many kinds and varieties of earth* that are used for the loam compositions for making the moulds for casting bronze, brass, or other metals. Since this is a very necessary thing, you must try to have the best kind and one that resists the fire well. It must be disposed to receive the metals well, must make a neat casting, and must not shrink or break with cracks on drying or baking. Aside from actual trial, I believe that there is little that can help you, since the clay in itself has no color or [77] visible sign that I know of to show how satisfactory it is. Understand that their colors are no less varied than their natures, for, as you see, one is white, one black, one yellow, and another red. Perhaps none will show by its color that it is good for this work, yet it might also happen that all colors are good. But all that I can say about it is to show you by their effects how the good ones should be in their nature; and so by trial you will choose among those that come into your hands. All earths are either sandy or tufaceous, either argillaceous and lean or pasty with unctuous viscosity. The lean ones make the loam powdery and without toughness and hold together poorly by themselves when they are dry. The unctuous and viscous ones shrink and break. Becoming smaller by shrinking, they often twist the forms and they stick together badly. They swell up again in the fire and produce works that are neither exact-a nor neat. Therefore, the good ones must be those that are neither unctuous nor lean, neither wholly tender nor rough, and with a grain that is fine, without pebbles or shells. When applied to a work they easily dry out without fractures and, when dry, hold their own shape well. Above all they must resist the fire well. These are usually of a yellow or red color, but whatever their color may be, the color does not force me to say that the yellow are really better than the black, and the red than the white or gray. Their quality depends on what trial shows. Thus, to summarize, whenever you have to do this work, you must try to have the best clay that you can, because it is to be the foundation of

Jan 1, 1942

Jan 1, 1929

By D. E. Musgrove

The question of alternating current vs direct current has become an important consideration to the mining industry. Rising production costs demand lower investment, which, in many instances, can be realized by the use of ac mining machines. Generally ac motors, control systems, and distribution and power conversion equipment can be installed for approximately 50 pct of the first cost of their dc equivalents. This basic saving has made ac mining a serious competitor for the traditional dc mining systems. With the increased use of ac voltages underground, there has developed the problem of conveniently converting distribution voltages to usable 480-v power. Power at low voltages should not be carried for comparatively long distances, and the transformation should be made at the point of use. Otherwise, serious voltage regulation problems and objectionable line losses will occur.

Jan 5, 1955

T. T. READ, Secretary of the Committee on Industrial Organization, presents the following very interesting monthly ad interim report: Reports from London are to the effect that 750 housing schemes for workers, involving the erection of 128,000 new dwellings, have been submitted to the Local Government Board. Birmingham alone needs 14,000 new houses, and the Housing and Town Planning Committee of the City Council considers that 5000 new houses must be built each year for the next 20 years. Nine hundred acres of land has been acquired, on which to build 10 to 12 houses per acre for the next two years. The town of Dudley, which built 300 modern dwellings in 1915-1916, submitted schemes for another 500 houses. There is a shortage of building materials required, specially brick. Financial assistance has been received for reopening brick yards that were closed during the war. W. E. Dickson, vice president of the Midvale Steel & Ordnance Co., is reported in the daily press as stating that his corporation is planning to spend $8,000,000 in improving its plant and assisting its employees in building their own homes. The company will advance 90 per cent. of the cost of the house and extend payments over a period of 12 years. Methods of work employed in building 256 houses at Quincy, Mass., for the workers of the Fore River shipyards are described, by Joseph Meltzer, in the Engineering News Record for May 29, 1919. The approximate cost was about $3500 per house, not including water supply, sewers, streets, and sidewalks. "Comparative Costs of Tenantry and Home-Owning;" "A Plain Talk on Helping Home-builders;" and "More Plain Talk on Home Building" are the titles of three publications of the Information and Education Service of the Department of Labor. These publications should be' of a good deal of service in convincing employees that it is to their interest to own their homes rather than to live in rented houses. The same Service has issued pamphlets discussing the cost of materials.

Jan 7, 1919

The problem of applying instrument control of variables associated with lead-zinc ore treatment has been under investigation for several years at The Zinc Corp. facilities in Broken Hill, Australia. In 1959 it was decided that there was sufficient knowledge of the problem to enable specifications to be drawn up for a system to automatically control at set conditions the roll crushing, ball milling, lead flotation and zinc flotation sections. In choosing between electrical and pneumatic control systems the broad principle was adopted that if the sensing system was pneumatic the transmission and control would also be pneumatic, whereas if electrical sensing was employed, electrical transmission and control would apply. In general. pneumatic systems were preferred owing to lack of experience with, and standardization of, the electrical systems offered at the time the specification was prepared.

Jan 12, 1964