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By K. A. Johnson, H. F. Yancey

Physical properties have been used for a long time in characterizing different kinds of coal, and such physical properties as friability and slacking have been included along with chemical properties in grouping coals according to the widely used system of classification adopted by the U. S. Geological Survey. Nevertheless, the usefulness of physical properties for classifying the different ranks or kinds of coal has been limited because it has not been possible to express these properties in definite form as numerical values. Because of the present wide interest in the formulation and adoption of a satisfactory system of coal classification, the Northwest Experiment Station of the U. S. Bureau of Mines, in cooperation with the College of Mines of the University of Washington, has recently completed a study of the physical and chemical properties of approximately 100 different coals ranging in rank from lignite to anthracite. Purpose and Scope For this investigation samples were collected in approximately 45 mines and prospects in Washington and 23 mines in other states. The following studies, in addition to proximate and ultimate analyses, were made of the samples: Determination of (1) friability, (2) slacking or weathering characteristics, (3) yield of products by low-temperature carbonization in a laboratory retort, and (4) agglutinating value. Most of the coals examined were subjected to each of the tests enumerated, but with coal of some ranks this was unnecessary in some instances, and in others it was not feasible to do the work involved. A report which includes the analyses of the coals and the details of the methods of examination used in the investigation is being published by the Bureau of Mines.' It is the purpose of the present report to show the results of the friability, slacking, low-temperature and agglu-

Jan 1, 1932

By W. B. Lilienthal

A considerable saving in time and money has been effected by use of a specially designed stainless steel container for laboratory drilling mud test work. This container involves use of a standard tall-form stainless steel beaker for service in which the mud sample is heated to an elevated temperature and maintained there for protracted periods of time, while undergoing agitation to facilitate mixing of mud components. Agitation is accomplished by rotating the filled containers on motor-driven rollers within an oven. Several porcelain balls are generally placed in the containers to further improve agitation. Soft glass containers (.Mason jars) were used in this service in early work, and were found to be unsuitable for the following reasons: 1. Poor resistance to thermal shock. 2. Containers could withstand only relatively low pressures. 3. Accidental breakage in handling. 4. Chemical deterioration and subsequent mud contamination from reaction of high pH muds with the glass at elevated temperatures. Pyrex containers were also considered, but, inasmuch as they provided improvement only in items 1 and 4 listed above the additional cost was not believed to be justified. A scale drawing of the container is shown in the figure illustrating details in cross-section. A pressed stainless steel lid was fabricated to match the rolled edge of the beaker

Jan 1, 1950

By F. G. Robb, D. N. Madge

This paper details some of the specifications and problems associated with implementing on-line control of a potash concentrator. The computer system described has the capability of three levels of control, including DDC with a single central processor. The system is also capable of on-line program compilation and modification through an extension of vendor utilities. The system is now in operation.

Jan 1, 1969

By N. H. MacMillan, W. M. Mularie, R. E. Jackson, A. R. C. Westwood

The initial results of a study of the environment-sensitive microhardness and diamond rotary drilling behavior of granite and its constituent minerals quartz and feldspar (microcline)1 have established that many similarities exist between the environment-sensitive mechanical (chemomechanical) behavior of these materials and that of the simpler solids such as periclase, soda-lime glass, and alumina4 studied previously, at least as far as n-alcohol (straight-chain alcohol) environments are concerned. The results of this study (hereafter designated study I) also suggested that the rate of drilling of granite in these environments is controlled by the chemomechanical behavior of its quartz constituent, and is greatest in those environments which impart a zero l-potential to this phase, thereby maximizing its hardness. Now, cationic surface-active species strongly influence the l-potentials of silicate minerals. For this reason they are widely used in mineral separation operations. In particular, dodecyl trimethyl ammonium bromide (DTAB) was found in study I to produce f 0 for quartz at a concentration in water of 107 to 10-4 moles per 1. Accordingly, the influence of dilute aqueous solutions of this surfactant on the drilling behavior of granite also was examined in study I. This revealed that granite could be drilled three to four times faster in 10-° molar aqueous DTAB than in water, and confirmed by experiment the suggestion that granite is most effectively drilled with a diamond core bit in environments which impart a zero l-potential to quartz. According to O'Connor and Buchanan' however, the isoelectric point for quartz in aqueous DTAB solutions occurs at a concentration of .•.•2 x 10-° moles per 1, rather than [101 to 10-1] moles per 1. To confirm the results of study I, therefore, a more comprehensive investigation of the [ ]-potentials of quartz, microcline, and Westerly granite in aqueous DTAB environments has now been undertaken. At the same time an examination has been made of one of the basic assumptions of the current conceptual understanding of chemomechanical effects. In this view, although hardness changes occur essentially instantaneously following wetting of the solid, they are confined to a surface layer at most a few micrometers (µm) deep. Hence, to maximize the influence of chemomechanical effects on bit penetration rate only shallow cuts should be taken. Practical penetration rates are then obtained by increasing bit rotation speed. Experimental l-potentials were determined by the streaming potential technique using an automated rapid-cycling apparatus recently developed by Martin Marietta Laboratory from a design by Somasundaran and Kulkarni. The drilling studies employed 3.2-mm-OD 120-grit diamond-loaded core bits with a wall thickness of ~0.7 mm, and bit rotation speeds of 2200 and 25,000 rpm. The load applied to the bit was independent of the depth drilled in both cases. The 2200 rpm measurements employed the same drill press and puddle drilling technique as used in study I. The higher rotation speed was obtained using a water-driven dental turbine drill. In the case, the surface active fluid was pumped down the axis of the bit to ensure efficient wetting and flushing of the drilling debris from the hole. In both cases drilling rate was measured by the parameter D(200), defined as the average rate of bit penetration during the interval from 150 to 250 sec after drilling commenced.

Jan 1, 1976

By R. W. Nelson

Methods for determining permeability presented by W. D. Kruger3 in a paper entitled "Determining Areal Permeability Distribution by Calculation" have considerable merit. They can be expected to contribute significantly to analysis of flow in heterogeneous systems. Some rather subtle yet important conditions must be met, however, to assure that the computed permeabilities are correct. The conditions which insure a unique permeability distribution may have been overlooked in the method as proposed and presented in the subject paper. The subtlety of the special requirements may permit good agreement between computed and measured pressures in the reservoir; but the computed permeability may still be in error. The general theory and discussion of the requirements for a unique determination of the permeability distribution are presented elsewhere in more detail.7'8 Accordingly, only major features will be presented here in the notation of Kruger. GENERAL DESCRIPTION OF REQUIREMENTS A brief mention of the route to be followed in showing the special requirements may be helpful. The equation to be solved is a quasilinear, first-order, partial differential equation in the unknown permeability. This equation can be solved through an extension of Lagrange's method by reduction to a system of subsidiary ordinary differential equations. Through consideration of the identity of one of the Lagrange subsidiary differential equations with the stream function, a special interrelationship can be shown. The interrelationship has special significance with respect to the boundary condition. If the boundary function satisfies part of the subsidiary differential equation, no unique solution for the permeability distribution exists. In the physical problem this requirement for uniqueness indicates that the permeability measurements used as a boundary condition can not be along a stream tube. The boundary condition must be along a line, or series of lines, which completely traverse the region and pass through every stream tube.

By Kandalla Ravindranath, C. C. Patel

Studies of the adsorption of dialkyldithiocarbamates at the surfaces of galena and sphalerite have shown that characteristic contact angles are obtained at galena surfaces in the 7-10 pH range, whereas lower angles are obtained at unactivated sphalerite surfaces even at pH 71 Further, the angles at sphalerite surfaces progressively decrease with increase in pH. However, when sphalerite is activated with cupric sulfate, characteristic contact angles are obtained at pH 7 and beyond. This shows that galena and sphalerite can be selectively floated with dithiocarbamate collectors at pH 7 and beyond. Experimental Materials Ore: The lead-zinc ore for the present study was obtained through the courtesy of the Geological Survey of India from Dariba, Udaipur, Rajasthan, India. The average ore analyzed 15.5% lead, 11.6% zinc, 6.7% iron, 15.6% sulfur and 36.6% acid insolubles. The ore was crushed in a Denver laboratory rod mill and sieved in a Denver automatic sieve shaker to obtain a -200- to +250-mesh (Tyler standard) fraction. This particular size was chosen because it was conducive to good liberation of sulfide minerals, both from one another and from gangue minerals. Collectors: Dimethyl, diethyl, diisopropyl and diisobutyl dithiocarbamates were prepared and purified by the methods described by Klopping and Van der Kerk.2 A freshly prepared 0.03% dithiocarbamate solution in distilled water was used for flotation studies. Frother: A 0.03% solution of pine oil in ethyl alcohol was employed. Activator: 7.3 g of cupric sulfate pentahydrate were dissolved in 1 1 of water and used for the activation of sphalerite. Depressant: 16.0 g of zinc sulfate heptahydrate were dissolved in 1 1 of water and used for the depression of sphalerite.

Jan 1, 1972

By Rex O. McLellan

The formation of a monovacancy in a metal is simulated in an elastic model by the displacement of the surface of a small spherical cavity in a large elastic continuum. The application of linear elasticity to this distortion results in a well- known formula for the energy and an expression for the concomitant entropy change due both to the shear strain in the continuum and also to the dilation of the solid resulting from the boundary conditions at the surface of the solid. Elastic data (the sliear modulus and its temperature coelficient) are used to calculate the entropy and energy of formation for many metals. Despite the simplicity of the assumptions involved, the agreement between the calculated entropies and energies and experimental values is remarkably good. In recent years there has been a large increase in measurements of the absolute concentration of mono-vacancies in metals as a function of temperature. Hence new data for both the energy and the noncon-figurational entropy of formation of monovacancies has become available. Recent measurements&apos; of the anomalous (non-Arrhenius) self-diffusion in many bcc metals has also focused interest on the prediction of the thermodynamic parameters of mono- and multi-vacancies in those metals for which no data are available. Damask and Dienes&apos; have discussed the various theoretical calculations of the energy of formation EL, of a monovacancy. These include simple models involving the breaking of atomic bonds on moving atoms from the interior of a crystal to the surface, models combining elastic calculations with surface-energy terms and detailed quantum mechanical calculations. The simler models give the correct order of magnitude of &, but tend to overestimate it by a factor of about two. The quantum mechanical calculations4"7 have been carried out for the noble and alkali metals with generally reasonably good agreement with the available Ef data. The calculation of entropy of formation Sfv14 lnvolves a fundamental calculation of the perturbation of the phonon spectrum caused by the creation of a vacancy. Huntington, Shirn. and wajda8 have given an approximate evaluation of sJV by considering an Einstein model for the localized vibrations in the immediate neighborhood of the defect and then using elastic theory to calculate the entropy associated with the shear stress field in the distorted crystal (as originally proposed by Zenerg). They also included a term due to the dilation of the crystal. They obtained a value of 1.47k for copper, in good agreement with the experimental value (1.50k). However, Nardelli and Tetta- manzi1° have recently shown that neglecting the coupling between atoms (Einstein Model) may lead to a serious error so the agreement may be somewhat fortuitous. In this work simple linear elastic theory is used to calculate the entropy and energy of formation of mono-vacancies. Despite the simplicity of some of the assumptions involved, the agreement with the available experimental data is remarkable. However. the reasonable degree of success in the application of linear elastic calculations to the excess entropy of a solute atom in a dilute solid solution1&apos; indicates that the application of elastic theory to vacancies. where the interaction of different atomic species is not involved, may not be inappropriate. THE ELASTIC MODEL The metal is assumed to be a spherical elastic continuum. A small spherical cavity of volume V = 4i;v:&apos;/3 is cut from the center. removed. and dissolved rever-sibly in the bulk of the material. TO a good approximation no net atomic bonds are broken and the material does not undergo a volume change although the externally measured volume of the body would increase by V. The radius of the sphere of metal is much larger than r Next a negative pressure is applied to the cavity causing its surface to be displaced inward by an amount simulating the relaxation of the lattice around a monovacancy. In this model the energy and entropy accompanying the distortion are taken as 4, and <. As a first approximation the equation of state for the solid is taken as: r = ro(i + *~D LiJ where K is the bulk modulus. P the hydrostatic pressure. Vo the volume of the material at 0°K and zero pressure. and d+/dT = 30. where 0 is the linear thermal expansion coefficient. The variation of entropy with hydrostatic pressure is given by the Maxwell equation: These equations give the entropy change resulting from increasing the hydrostatic pressure from 0 to P as: and since • we have: This is the entropy arising from the dilation resulting

Jan 1, 1970

By A. T. Schwennesen

Every engineer has occasion to trace or copy a map, plan, or other drawing on paper too thick for the ordinary way of using tracing-cloth or tracing-paper. When the figure is small and simple a copy may be made by holding the original against a window-pane, coverin& it with the paper, and tracing direct by the aid of the strong sunlight from outside. The need of utilizing this principle on a larger scale and in a more convenient position led Dr. J. C. Branner to plan the table of which the following is a description : This table was first made in the form of an adjustable glass-top table with a mirror beneath, in 1887, while Dr. Branner was State Geologist of Arkansas. Later it was modified as experience suggested until the form as here described was evolved. The device consists essentially of a drafting-table with a plate-glass top, upon which the original drawing and the paper are laid, and a mirror mounted underneath to reflect the light of the sky up through the drawing. The glass top is hinged and fitted with two arms and thumb-screws, so that it can be raised and fixed to any position, either inclined or horizontal. The mirror is pivoted and revolves about a horizontal axis, so that it may be tilted to any angle. The hood of cardboard or black cloth prevents the reflection of light from the tracing, and may or may not be attached to the table.

Jan 1, 1912

By G. S. Hume

The largest development program in the history of Alberta was undertaken in 1941 in an effort to increase oil production. The drilling record is as follows: In Alberta there was the largest exploratory campaign for oil in the history of the Province, although drilling of wildcat wells was somewhat less than in the previous year. A great deal of geophysical work was done. This included three gravimetric and five seismic parties as well as a number of geological survey parties by the major oil companies and by the Geological Survey of Canada. Seismic work was done by one party in southern Saskatchewan. The production of petroleum in Canada is shown in Table I. About 98 per cent of the total production comes from Alberta and the yield of the various fields is shown in Table 2. The greatest developments in Turner Valley have been in the north end. In 1941 about two miles of new productive area was proved by drilling, extending the field to a length of 20 miles. The wells at the

Jan 1, 1942

By G. S. Hume

The largest development program in the history of Alberta was undertaken in 1941 in an effort to increase oil production. The drilling record is as follows: In Alberta there was the largest exploratory campaign for oil in the history of the Province, although drilling of wildcat wells was somewhat less than in the previous year. A great deal of geophysical work was done. This included three gravimetric and five seismic parties as well as a number of geological survey parties by the major oil companies and by the Geological Survey of Canada. Seismic work was done by one party in southern Saskatchewan. The production of petroleum in Canada is shown in Table I. About 98 per cent of the total production comes from Alberta and the yield of the various fields is shown in Table 2. The greatest developments in Turner Valley have been in the north end. In 1941 about two miles of new productive area was proved by drilling, extending the field to a length of 20 miles. The wells at the

Jan 1, 1942

Assistant Professor of Mining Engineering.-Mining engineer to teach mine surveying, mine mapping, assaying, etc., but not metallurgy. Location, Ohio. Salary, $1800 per annum. No. 379. Metallurgist.-Experienced metallurgist capable of running 25-ton blast lead furnace. Man who knows the country and speaks Spanish desired. You may know that this state is in peaceful conditions and that even during the worst time of the revolution there were several mining concerns never idle. Besides, its resources are wonderful, and once a man gets started, he will find many possibilities. Notwithstanding that Sinaloa is a mining state, our smelter will be the only lead smelter on this coast. Location, Culiscan, Sin., Mexico. No. 381. Quarry Superintendent.-Engineer experienced in limestone quarry work for position as superintendent; must be capable of producing results; must increase output of quarries from 4 to 12 cars per day. Young man with abundant energy is desired. Permanent position, chance to grow up with the company. Location, New Jersey. Salary depends upon the man. No. 382.

Jan 4, 1919

By G. Kinder, R. Gilges, W. Stoker, R. Davey

The Bingham Canyon Mine, located 48 km (30 mi) southwest of Salt Lake City, Utah, is operated by Kennecott Copper Corporation&apos;s Utah Copper Division. This operation is the world&apos;s largest open-pit copper mine and produces 96 000 tons (106,000 st) ore and 327 000 tons (360,000 st) waste each day. This material is loaded by large electric shovels and transported by both truck and rail haulage. To meet the requirements of the Clean Air Act of 1970 (as amended), new facilities for the control of smelter emissions were required and are now nearing the final stages of construction. The facility will be capable of treating all the output from the mine, some 2,530 tons (2,789 st) per day of combined concentrate and precipitate. Costing $280 million and necessitating the replacement of reverberatory furnaces with continuous smelting vessels, the plant, with its massive and complex gas handling and acid-making facility, is required to remain on-stream with the minimum of pollution control equipment outages to conform with Federal Regulation 52.2325.

Jan 8, 1978

By Harrison, Henry Fay

The study of an entirely new series of alloys may be undertaken from a desire to obtain knowledge applicable to the perfection of industrial alloys, or merely to test certain theoretical considerations. In the case of antimony-tellurium alloys, the theoretical side only is at present important; but it is hoped that the results of this investigation may have some industrial value, at least indirectly, by furnishing one more example for comparison when studying commercial alloys. The statement is found in various places that antimony is isomorphous with arsenic, bismuth and tellurium; but very little experimental evidence has been offered in support of this assumption. All four metals crystallize in rhombohedra, and the ratio of the axes a: c is approximately the same—which seems to indicate, but does not prove, their isomorphism. The close association of these metals in minerals also seems to indicate that they are isomorphous. There are, however, certain differences in their properties which render this coriclusion somewhat doubtful, and it is therefore desirable that inde-

Jan 1, 1902

By J. L. Brimhall

Slip-line formation during bending has been studied on neutron-irradiated molybdenum single crystals. For equivalent strains, the slip lines are coarse and distinct in the irradiated molybdenum and not resolvable in the unirradiated molybdenum. The slip lines have been directly correlated with dislocation channels present in the irradiated and deformed thin foils. The heterogeneous distribution of the dislocations during deformation in the irradiated material results from dislocation interaction with the dejects produced during irradiation. Impurities , in the form of&apos; carbides, affected the dislocation channeling Principally by acting as dislocation sources. ALTHOUGH the mechanical behavior of irradiated materials has been studied extensively, the precise mechanism of irradiation hardening has not been established. Some information on the microstructural species responsible for hardening of irradiated materials has been derived from direct and indirect observations. The direct observation of the structure of deformed irradiated metals, particularly by transmission electron microscopy, is a relatively new and unexplored area. Slip-line studies in fcc metals have been restricted primarily to copper.1-3 Very coarse slip lines, representing slip on many closely spaced planes, have been observed in deformed, irradiated copper. Coarse slip lines have also been observed in irradiated aluminum.4 Clear channels in irradiated copper caused by dislocation motion through the defect structure have been seen by transmission electron microscopy and correlated with slip lines.5-6 To date, little work has been reported on the irradiated bcc metals. Eyre described the slip lines around hardness indentations on irradiated iron and found them to be more distinct than lines in unirradiated material.&apos; Mastel et al.&apos; have observed channels in deformed irradiated molybdenum similar to those reported in copper. As part of a program concerned with the effect of neutron irradiation on metals, the slip-line

Jan 1, 1965

By Andrew A. Blair

It is now well known that certain pig-irons give a considerably smaller percentage of sulphur when determined by evolution-methods than when determined by oxidation-methods. The most striking examplcs of such irons are those made either wholly or in large part from New Jersey magnetites containing more or less titanium. It is never safe to use an evolution-method on such iron; for it is quite common that the sulphur result by evolution is only one-half or even one-third as great as that obtained by oxidation. For this reason, evolution-methods should be discarded, except in the analysis of pig-irons known to contain the sulphur in a state of combination from which it is evolved as sulphuretted hydrogen on treatment with hydrochloric acid. A good example of an iron containing, in the residue, sulphur insoluble in hydrochloric acid having come to our attention, it was determined to try to isolate a suspected insoluble sulphide. A large piece of high-silicon gray-forge iron was accordingly selected as the most promising material to work on. This piece was dissolved slowly, through several months, in dilute hydrochloric acid, aided by the electric current, yielding a soft graphitic residue. The object of dissolving a mass of iron, instead of drillings, was to prevent the crushing, by the drill, of any insoluble crystalline compound that might be present. The first step in the preparation was to break up the graphitic material and put it through bolting-cloth of 157 meshes to the linear inch. This was done by crushing the mass under the fingers on the bolting-cloth fastened over the top of a beaker, while a stream of water from a wash-bottle washed the finer portions through the cloth. The suspended matter was allowed to settle. It was then transferred to a platinum

Jan 1, 1902

By Robert S. Shoemaker

Recently we read a short article which stated that Marcona Corp. was studying the use of 25,000-hp autogenous grinding mills for an iron ore project in Alaska. As if that weren&apos;t enough, they were going to dispense with the primary crusher and feed run-of-mine ore to the grinding mills which were to be driven by wrap-around seven-cycle motors. We see also that Bougainville Copper Co. will be grinding 90,000 tpd of ore in only eight 4250- hp ball mills. At Bougainville too, their float section will be the first large one to be completely equipped with the new 350-cu ft flotation cells. After a half century of relatively peaceful growth in the minerals industry, we are now seeing almost exponential advances in both equipment and plant size. At the same time, we are seeing a constant blending of hydro and pyrometallurgical techniques and processes into minerals beneficiation until the sample grind-&apos;em-up-and-concentrate-&apos;em plant is becoming a rarity.

Jan 1, 1970

Jan 1, 1918

By C. P. Parsons

CALIPER logging is a practice of measuring the variations in the diameter of the open hole in a well. This information is useful for many purposes, among which are: Determining the volumetric capacity of the portion of open hole to be cemented; the amount of gravel to be used for gravel-packing a well; the size and location of seat for a packer to be placed in a well; studying the effects of nitroglycerin shots; studying the effects of acidizing; studying the cause of drill-pipe failures; studying drilling technique; geological correlations. This is a new practice in oil fields and is eliminating considerable guesswork.

Jan 1, 1942

By W. A. Mudge, Paul D. Merica

One of the most prominent features of our present-day industrial development is the ever-increasing demand put upon materials of construction. Engineering ingenuity, within the past 25 years, has been unusually active, and in some fields at least engineers frankly say that engineering design has progressed as far as the limitations imposed by the properties of the present materials of construction will permit. Consequently, they are today demanding improvement in their working materials and seeking new ones, through the aid of which the present limitations of design may be overcome. The activity of this search is evident in all fields, but it is particularly so in that of structural materials required to be resistant to corrosion. The corrosion resistance of metals and alloys is never absolute and all-inclusive; a particular alloy will withstand some corrosive conditions well and fail utterly under others. Furthermore, other properties, physical and mechanical, required in conjunction with corrosion resistance vary considerably for different commercial applications. One wants a soft, ductile sheet metal resistant to atmospheric corrosion; another, a high-strength alloy resistant to sulfuric acid. The last decade has witnessed active and definite progress in the development of high-strength, corrosion-resisting alloys. In June, 1924, a symposium by the American Society for Testing Materials, on Corrosion-resistant, Heat-resistant and Electrical-resistance Alloys, disclosed no less than 60 commercial alloys the properties of which were described as being suitable for industrial service where corrosion resistance was a feature. Today the number of these alloys has been doubled, at least. In addition, economy in design and construction through decreased weight has given considerable impetus to the improvement of alloys of which the mechanical propprties may be improved by heat-treatment.

Jan 1, 1935

By Paul D. Merica, W. A. Mudge

One of the most prominent features of our present-day industrial development is the ever-increasing demand put upon materials of construction. Engineering ingenuity, within the past 25 years, has been unusually active, and in some fields at least engineers frankly say that engineering design has progressed as far as the limitations imposed by the properties of the present materials of construction will permit. Consequently, they are today demanding improvement in their working materials and seeking new ones, through the aid of which the present limitations of design may be overcome. The activity of this search is evident in all fields, but it is particularly so in that of structural materials required to be resistant to corrosion. The corrosion resistance of metals and alloys is never absolute and all-inclusive; a particular alloy will withstand some corrosive conditions well and fail utterly under others. Furthermore, other properties, physical and mechanical, required in conjunction with corrosion resistance vary considerably for different commercial applications. One wants a soft, ductile sheet metal resistant to atmospheric corrosion; another, a high-strength alloy resistant to sulfuric acid. The last decade has witnessed active and definite progress in the development of high-strength, corrosion-resisting alloys. In June, 1924, a symposium by the American Society for Testing Materials, on Corrosion-resistant, Heat-resistant and Electrical-resistance Alloys, disclosed no less than 60 commercial alloys the properties of which were described as being suitable for industrial service where corrosion resistance was a feature. Today the number of these alloys has been doubled, at least. In addition, economy in design and construction through decreased weight has given considerable impetus to the improvement of alloys of which the mechanical propprties may be improved by heat-treatment.

Jan 1, 1935