Search Documents

By F. D. DeVaney

Metallurgists and coal-washing engineers have used heavy liquids for years in studying the characteristics of ores and coal. By such means true separations can be made between the various specific-gravity increments in the materials examined. To use of heavy liquids has permitted determination of the possible grades of tailings and concentrates by specific-gravity methods on any particular size, and therefore the size to which the ore must be crushed to free the valuable material. The simplicity of float-and-sink separation and the high degree of efficiency attained in the laboratory are factors that commend the method for commercial concentrations.

Jan 1, 1940

By G. F. Tagg

In an earlier paper1, the author described a method of interpreting earth-resistivity curves, based on the theoretical investigation of a single horizontal underlying stratum. If the four-electrode system of Wenner is employed, the resistivity in a homogeneous soil is given by the formula where a is the electrode separation and R is the resistance of the earth between the two inner electrodes. If the earth is not perfectly homogeneous, the application of this formula gives an apparent specific resistance varying with the electrode separation. In the special case of the single horizontal underlying stratum, there is a surface layer of thickness h and resistivity p1 and a lower layer, extending to infinity, of resistivity pz. It has been shown by Lancaster-Jones2 that the apparent resistivity obtained by an application of equation 1 is related to the true resistivities, the depth h and the electrode separation a by an expression of the formhere pa is the apparent resistivity and F is a function (actually an infinite series), of the ratio h/a, and a reflection coefficient k = (p2 — p1)/(p2 + p1). For given values of h/a and k, the right-hand side of equation 2 can be calculated, and curves drawn showing the relationship between pa/p1, h/a and k. Such a set of curves for the case when p1 > p2 is given in Fig. 1. When pl is less than pz it is more convenient to use conductivity instead of resistivity. Hence, if oa = the apparent conductivity = lip, and a1 = the conductivity of the upper layer = l/pl, it follows that GeophyGical prospecting by earth-resistivity methods is frequently applied to investigation of structural problems in geology. Fig. 1 indicates a scheme of the general arrangement used in these methods of measurements. The battery (or generator) E is connected with two "current electrodes" I1 and I2. The current of intensity J, supplied by this battery, passes through the earth between these elcc- trodes. A potential difference U will be measured between two other electrodes V1 and Vz, called "potential electrodes." According to the configuration of electrodes (Fig. I), the resistivity of a homogeneous soil results from the formula

Jan 1, 1940

By L. L. Wyman

The resultant embrittlement caused by the exposure of oxygen-bearing copper when hot and exposed to reducing gases has been the subject of many studies.' Little attention, however, has been given to the possible embrittling effects due to atmospheres or conditions that under some circumstances might be the source of a reducing gas. At rather infrequent intervals there occur reports of copper becoming embrittled during normal annealing cycles in commercial steam-atmos-phered furnaces such as customarily are used for this operation. As might be expected, several other factors exist—such as oil, dirt on the wire, or in the furnace, or metallic surface contacts—that might produce reducing gases and be the source of the trouble. However, in consideration of the statement made by Ruder,2 it would seem that under some conditions steam itself might prove to be the source of trouble. A consideration of the amount of the dissociation of water vapor up to temperatures of the melting point of copper shows that3 the amount of hydrogen that could come from this source is far too minute to account for any embrittlement. What such information does not tell is what will happen at the surface of copper when subjected to steam at elevated temperatures, for entirely different conditions may persist, which would account for Ruder's observation. Furthermore, there are no data as to what might happen at the surfaces of other materials present, the resultant of which might affect the condition of the copper present. For this reason, it was decided to make a series of experiments comparable to those previously conducted by the writer,' which would clarify the effect of the steam on copper, and in copper in the presence of steel. Material The material used in these experiments was tough-pitch copper wire of rectangular cross section, about % in. thick, picked at random from the regular factory production of material used for windings, etc., in the electrical industry. Chemical analysis of this material gave the follow-

Jan 1, 1940

By C. F. Quest, T. S. Washburn

The steel industry has a definite need in its tonnage mills for a formula relating expected tensile strength to the analysis of the steel. The McWilliam-Barnes1 and other less comprehensive formulas are used for this purpose, but these formulas were designed for an analysis range that does not include the medium manganese and silicon-bearing steels. This type of steel is being produced to meet the demand for tensile strength slightly higher than that of ordinary structural steel but not high enough to justify expensive alloy steels. The purpose of this paper is to present a somewhat more comprehensive formula based on data accumulated over a number of years by the Inland Steel Co., and to discuss the method followed in obtaining a formula to fit the data. The resultant formula admittedly is still weak in some respects, but for the expanded analysis range appears to be an improvement over the other formulas. It is hoped that with the collection of more data and possible collaboration with other mills studying this problem it will be possible to work out a more nearly perfect formula. Several publications have been issued on this subject. In some, the equation type of relation was evolved while others made a combination of tables and an equation. The latter include work by Campbel12,3 and Webster.4,5 Campbell classified the steels as acid and basic and applied a different formula to each. For basic steels, he used the equation: Teosile etrength = 41500 + 770C + 1000P + yMn [1 y was a variable depending on the carbon and manganese content of the steel and was listed in tables. Webster investigated acid Bessemer steel and developed the equation: Tensile strength = 38000 + 800C + xTP+ yMn [2]

Jan 1, 1940

[This is the eighth in a series of reports on properties of commercial motor fuels, made in accordance with a cooperative agreement between the Cooperative Fuel Research (C.F.R.) Committee and the Bureau of Mines of the United States Department of the interior. The fir t report gave data on motor gasolines sold during the winter of 1935-36.3/ The present report, covering 1,679 simples, represents the products of US companies plus those from the Pacific coast, witch were averaged by the Pacific Coast Technical Group before being submitted and arc published exactly as they were submitted. The three groups of data on samples of regular, premium, and third-grade gasolines are averred separately. the, number of samples and brands representing each grade are as follows: Regular price, 869 samples, 76 brands; premium price, 452 sample, 45 brands; third-grade 358 samples, 52 brands. In this report the same marketing districts are retained as were used in the preceding report, and as for as possible the actual sampling points in each area are indicated on table 1.]

Jan 1, 1940

By Arthur C. Simmons

Oil production and activity in northern and central Pennsylvania was slightly less in 1939 than in the previous year, but owing to higher average prices 1939 was undoubtedly a better business year. The last quarter showed markedly increased activities throughout all of the Pennsylvania fields. Production, Stocks and Price Storage of Pennsylvania crude oil at pipe lines and refineries totaled 5,413,000 bbl. on Dec. 31, 1938, and declined during the year 1,124,000 bbl. to a total of 4,319,000 bbl. at the end of 1939. The stocks of crude at the end of the year represent the lowest point reached in Pennsylvania-grade crude storage in recent years. Stocks increased slightly during April, May and June, but decreased during all other months of 1939. The Bradford field production within the state of Pennsylvania averaged 35,340 bbl. per day throughout 1939, which represents a decrease of 1419 bbl. a day from the 1938 average. The production in central and southern Pennsylvania increased 1176 bbl. per day, averaging 12,159 bbl. throughout 1939. Table 1 includes annual production for the part of Bradford field situated within the state of Pennsylvania, for central and southern Pennsylvania, and for the entire state of Pennsylvania. A definite segregation of production between the Bradford field and central and southern Pennsylvania is slightly ambiguous because a portion of the oil from the newly discovered Music Mountain pool is included statistically in each area. In all probability the entire increase and some small addition to the production from southern Pennsylvania can be attributed to oil produced from the Music Mountain pool. Within the Bradford field, six price changes occurred throughout the year. At the beginning of 1939 the price of Bradford crude oil was $1.80 per barrel, whereas by the end of the year it had risen to $2.50. The weighted average price for Bradford crude during 1939 was $2.059 per barrel.

Jan 1, 1940

Page Laboratory Methods...........................127 Special Analytical Methods.......................127 Improvements in the Accuracy of the Vacuum-fusion Method for the Determination of Oxygen in Steel....................127 Quantitative Spectrochemical Analysis of Mixtures of Gases.......131 Oxygen Samples from Open-hearth Bath...............133 Rapid Analysis of Sample for Alumina.................139 Accurate Carbon Analyses in Low-carbon Steel.............139 Laboratory Technique for Study of Reactions Involving Liquid Metal. . . . 142 Rotating Liquid Crucibles......................143 Stationary Crucibles.........................145 Jones and Laughlin Experimental Furnace...............148 Vacuum Melting..........................149 Measurement of Temperature of Liquid Iron and Steel;..........149 Pouring and Teeming Temperatures..................149 Bath Temperatures.........................151 Plant Methods.............................154 Methods of Studying Slags.......................154 Sampling Slag in the Open Hearth..................155 Viscosity of Open-hearth Slags....................155 Petrographic Examination of Slag...................156 Statistical Methods Applied to Study and Control of Chemical Relations in Bath...............................166 Rapid Method of -Correlation Applicable to Study of Steelmaking Reactions............................166 INTRODUCTION On Thursday morning, Feb. 16, 1939, a round table discussion was held on the subject of Experimental Methods in the Study of Steelmaking. Dr. John Chipman, Professor of Metallurgy at the Massachusetts Institute of Technology, and chairman of the A.I.M.E. Committee on Physical Chemistry of Steelmaking, presided. In opening the meeting, the chairman said: "The purpose of this round table is to discuss methods of study by which more and better information on the fundamentals of steelmaking can be obtained. It was thought that a round table discussion rather than a symposium would furnish the best opportunity for those actually using various methods of study to get together and discuss their common problems. For this reason attention will be focused upon methods of study rather than upon their results. We want new and current and up-to-date discussion.

Jan 1, 1940

By Gilbert Soler

PRODUCERS of alloy steels recognize the importance of chemical composition in rela-tion to the hot-working properties and the typical surface defects found in their prod-uct. Each analysis of steel has its own peculiar characteristics. Under conditions of standard mill practice each analysis is susceptible to certain types of defects. Mill practice must be varied to obtain the best combination of surface and internal quality in the product. Chemical composition influences the cast structure and crystallization character-istics of the ingot. It also determines the rate of heating and cooling, the plastic hot-working range, and the phase structure of the steel at various temperatures as well as the tendency toward scale formation and decarburization, This paper endeavors to emphasize the manner in which chemical composition affects the various properties of steel, and to indicate the relative impor-tance of these factors in relation to the hot-working properties and surface charac-teristics of killed steel. The influence of chemical composition may be outlined as follows: I. Effect on the cast structure of steel, including: A. State of deoxidation, and type of inclusions. B. Gas content of steel. C. Freezing point and melting point of steel.

Jan 1, 1940

By M. G. Cheney

THE production record of the Sinclair-Moren pool, in southeast Young County, Texas, demonstrates that under efficient operating methods a single well may obtain normal oil recovery from an area of 100 acres or more. This record is the more surprising in view of relatively adverse reservoir conditions such as lack of water drive, moderate initial reservoir pressures and a consolidated sandstone reservoir with original permeability greatly reduced by processes of lithification. This case history is considered worthy of special study in view of the ever present problem of proper spacing of wells. Cupidity, abetted by the unrestrained law of capture, has in too many instances guided development and production methods without regard for sound economic and engineering principles. Largely as a result of ill advised spacing of wells, many oil fields have brought financial losses instead of deserved profit to those using capital, time and energy in this important business of adequately meeting the petroleum requirements of what is known as our modern civilization. In March 1923, the Sinclair Oil and Gas Co. obtained initial daily production of about 12,000,000 cu. ft. of gas and 1100 bbl. of oil in its first well near the center of a 372-acre lease on the L. P. Moren land, James Rose survey, Abstract 245. This exploratory test was drilled as a geological prospect of average promise, on a plunging anticline with possibly 10 ft. of closure as mapped on the outcropping limestone of upper Canyon (Pennsylvanian) age. In subsurface, the top of the producing res-ervoir is 16 ft. lower in this well than in the highest wells but probably 25 ft. above lowest closing contour. Wells No. 2 and 3 were drilled about 1/4 mile west and southwest near a normal fault with some 30 ft. of downthrow to the southwest. The producing sand was reached at a depth of 2512 ft. and drilled to 2529 ft. in the first well. This sandstone reservoir is of Millsap Lake (middle Strawn, upper Cherokee) age. It was absent in the second and third wells, which were abandoned at the depths of 3725 or more. In April 1925, a fourth well was drilled 600 ft. east and 24 ft. lower for top of sand than No. I. Production of about 100 bbl. daily was reported from 2521 to 2562 after an 80-quart shot. This well was drilled to 4560 ft., plugged back to 2575 and shot again; but was abandoned soon thereafter because of small production.

Jan 1, 1940

By R. A. David, D. L. Katz, D. J. Vink

A phase diagram showing boundary curve and quantity of liquid in the two-phase region was determined for a mixture of natural gas and natural gasoline in the region of its critical conditions. The temperatures and pressures of phase measurements were in the range of 85 to 212 F. and 1300 to 2600 Ib. per sq. in., respectively, with the critical conditions at 169.5 F. and 2615 Ib. per sq. in. abs. Color phenomena were observed in the region of the boundary curve from 102' to 192 F. Approximate densities of the single-phase and two-phase regions and analysis of the system are included. Boundary curves between the single-phase and the two-phase regions have been determined for several binary mixtures containing hydrocarbons. 2,3,4.6,7,10,11,12,14 These investigators did not report the relative amounts of liquid and vapor within the two-phase region. The equilibrium values obtained from the dew-point and bubble-point data can be used to compute the lines showing percentage of liquid on the pressure-temperature phase diagram8 but the positions of the lines near the critical temperature and pressure are uncertain. Relative amounts of vapor and liquid were obtained for a gasoline and a naphtha1 within the two-phase area but not in the region of the critical temperature and pressure. The bubble-point and dew-point lines, as well as the percentage liquid lines within the two-phase region, were determined by visual observations in glass apparatus. Apparatus An arrangement of the apparatus is given in Fig. 1, showing the Jerguson gauge A with glass windows B. Pressure was supplied by the

Jan 1, 1940

Jan 1, 1940

By George R. Gardner, Kenneth B. Ray

The application of wet cleaning processes for the beneficiation of bituminous coal has created in some localities a problem in the recovery and disposal of fine solids in the washery water. The maximum allowable concentration of these solids in the washery circuit that is consistent with satisfactory operation of the cleaning units remains a controversial point. It has, however, been generally recognized for a number of years that some degree of control should be exerted over the concentration of such material. Early methods of control involved intermittent or continuous discharge of a portion of the plant slurry into near-by streams or settling ponds, and this persisted even after the adoption of settling tanks or cones. The practice is not always economical, for two reasons: first, because of the waste of coal, and, second, because it is sometimes difficult and expensive to obtain an adequate supply of water. The latter condition often is aggravated by chemical treatment of the make-up water that is necessary to prevent excessive corrosion of plant equipment. The modern approach to this problem has been the adoption of continuous thickening devices. However, because such equipment occupies considerable plant space and is somewhat expensive to construct, the practice of loading these thickeners beyond their rated capacity is widespread, therefore often the performance of such units is not altogether satisfactory. In recent years, European washeries have increased the rate of settling of the fine coal from the slurry by the addition of specially prepared starch solutions. These reagents cause flocculation of the solid particles and thereby increase the rate of sedimentation. The first important work on the flocculation and clarification of coal slurry was done by Henry, who developed the Henry process and used it successfully in Belgian preparation plants. Soon after the initiation in Belgium, the process was introduced into England, where subsequent investigation developed similar processes, which were successfully used in

Jan 1, 1940

By O. C. Wheeler

The total oil production from Colombia during 1939 amounted to 23,774,151 bbl., constituting a new high record. Of this amount the Tropical Oil Co. produced 22,374,151 bbl. from its De Mares concession and the Colombian Petroleum Co. produced 1,400,000 bbl. from its Barco concession beyond the eastern Andes. The Socony Vacuum Oil Co. produced a small amount of crude from its Las Monas wells north of the Sogamoso River in the Magdalena Valley for consumption on its own property, but this is not included in the figures given above. The South American Gulf Oil Co. provided the outstanding development in the country by the completion, late in the year, of its 12-in. pipe line from the Colombian Petroleum Company's Barco concession to the coast at Covenas. This was a notable accomplishment, achieved in the face of tremendous natural obstacles. With the completion of this line there are now two crude-oil outlets from the interior of Colombia to the coast, the other being the Andian National Corporation's line down the Magdalena Valley from Barranca Bermeja. The Barco property becomes the second major producing area in Colombia. The acquisition of prospectivc oil lands continued at about the same level as during the prcvious year. Most of the lands taken up or applied for had their subsurface rights vested in the National Government. Relatively little interest was taken in the leasing of privately owned lands. Tropical surrendered its Putana concession on the Sogamoso River after finding it to he nonproductive. The status of applications for National lands that had been accepbed or on which concession contracts had been awarded at the end of the year is shown in Table 3. In the Magdalena Valley wildcat drilling in the search of new fields was conducted to the east of Puerto Berrio by the Compania de Petroleo Shell de Colombia, Compania Coloinbiaila de Petroleos El Condor and by the Sociedad Nacional del Carare; further down the valley to the cast of Puerto Wilches, the Socony T'acuum was drilling two wildcats. No discoveries resulted from this exploratory work. On the Barco conces-

Jan 1, 1940

The Institute conducts jointly with the American Society of Civil Engineers, American Society of Mechanical Engineers and American Institute of Electrical Engineers, certain activities as listed below, and is joint owner with them of certain properties. United Engineering Trustees, Inc. When Mr. Carnegie made his gift which made possible a home for the engineering societies, a separate corporation was organized to act as a holding company and to manage the common property. This was long known as the United Engineering Society, but the name has now been changed to one which more nearly reflects the real function of the corporation. It holds title to the Engineering Societies Building and to various funds placed in its charge and is managed by a Board of Trustees, of which three are chosen by each of the four societies, American Institute of Mining and Metallurgical Engineers, American Society of Mechanical Engineers, American Institute of Electrical Engineers and American Society of Civil Engineers, which have equal and undivided interests in the property. The land and building cost two million dollars. During the year 1934, the Constitution and Bylaws of The United Engineering Trustees, Inc., were thoroughly revised and a better organization of its functions was effected: The Engineering Foundation and the Engineering Societies Library were made "departments" of the United Engineering Trustees. The Founders Societies share in the property which it holds, and estimated at the present time, as follows: Real estate, $1,993,793; Depreciation and Renewal Fund, $415,225. The U.E.T. has endowment funds amounting to $1,203,740. The A.I.M.E. trustees are W. D. B. Motter, Jr., A. L. Queneau and Albert Roberts.

Jan 1, 1940

By Fred Bond

WHEN some materials are ground dry in a ball mill, a stage of comminution is reached at which the finely divided particles begin to adhere to the balls and to the mill lining. As grinding progresses, a coating accumulates upon the grinding media, which tends to cushion the impacts and thus retard reduction of the material, and finally becomes so thick that all grinding ceases. At this stage, the characteristic noise produced by the grinding media dur-ing normal mill operation changes to a dull, muffled sound. In most instances, the formation of the coating marks the practical limit of size reduction. Industrial requirements for fine grinding frequently meet with this obstacle, and the tendency in many com-mercial operations to grind materials to a higher degree of fineness than formerly makes the solution of this problem an im-portant one. The phenomenon is of far greater importance, therefore, than the limited amount of research and technical discussion devoted to it implies. In order to learn more about the coating of different materials when ground dry to a high degree of fineness, certain labora-tory tests were made from which it was found that different materials form coat-ings at widely different size distributions. It is probable that most materials will coat if they are ground fine enough; the exceptions have inherent lubricating qual-ities, like coal and graphite.

Jan 1, 1940

By Mark C. Malamphy

The occurrence of outcrops of bituminous schists and sandstones impregnated with heavy asphaltie petroleum first directed attention to the São Pedro area as a possible source of commercial production of petroleum. Since 1920, more than 20 wells have been drilled in this area. The discovery of oil shows and small quantities of natural gas in some of the early wells led to the continuation of drilling in the hope that more important findings would result. During the early part of 1934, detailed magnetometer observations were made in this area, and a considerable number of torsion balance stations were occupied. The results of these geophysical observations help considerably to clarify the structure of the area and the very considerable amount of geologic information available makes possible a much more exact interpretation of geophysical anomalies. In presenting the results of these observations, and interpretation of the geophysical data, certain actual case problems are included; i.e., geophysical anomalies due to anomalous masses of which the forms and positions are more or less known. Although anomalies due to igneous intrusions are probably more important to geophysicists in Brazil than in other countries, these data have a certain interest for all geophysicists, particularly because they were obtained in the south magnetic hemisphere, where the lines of magnetic force are directed upward, and in a region of moderately low inclination. This is considered as a geological-geophysical problem, and only passing mention will be given to the petroleum possibilities of the area. General Geology The location and general geology of the São Pedro area are shown in the sketch map of Fig. 1, which is adapted from the geologic map of South Brazil compiled by Oppenheim1,†- who gives the geologic column of South Brazil (So Pedro and vicinity) as follows:

Jan 1, 1940

By Alden B. Greninger, Alexander R. Troiano

Metallurgists have long believed that martensite in steel forms as plates along the octahedral {111} planes of austenite. Much has been written about mechanisms whereby units of the austenite lattice are pictured as transforming to martensite by shearing movements initiated along the octahedral planes of austenite, supposedly resulting in plates of martensite lying parallel to these planes of shear. A critical inspection of two or three photomicrographs of quenched hypereutectoid steel led us to the conclusion that the orientation habit of martensite, at least in hypereutectoid austenite, could not possibly be octahedral. Inasmuch as recent studies,30,31 of the martensite-type reaction in nonferrous alloy systems have established the irrational orientation habit as characteristic of this type of lattice transformation, the need for a thorough restudy of the crystallography of martensite formation in steel was evident. The present paper reports the results of such a study, extended to include both cementite and some of the products of constant-temperature decomposition of austenite. Also reported are a few of the results obtained from a microscopic and X-ray study of the austempering process in very high-carbon steel. I. The Martensite Transformation Previous Work Microstructure and Crystal Structure of Martensite.—Among the best series of published photomicrographs of quenched steels are those of Whitely,1 Robertson,2 Hanemann and Schrader,3 and Lucas.4 The crystal structure of martensite is body-centered tetragonal, with axial ratio varying from 1 near 0.0 per cent carbon to 1.08 for 1.75 per cent

Jan 1, 1940

By Kenneth Eilerts

The development and operation of "combination wells"5/ have created new and unusual problems, many of which can he solved only if information is available concerning the properties of the fluids produced. Data as to the characteristics of the fluids at the relatively high pressures that exist in the reservoirs are especially important, and there is growing economic concern to know what part, if any, of the liquid recovered at the surface was liquid in the reservoir, As an extension of this problem, it is important to know, whether liquid will be formed in the reservoir as a result of isothermal retrograde condensation when the reservoir pressure is reduced. The pressure range of such condensation, if it occurs, is significant in the design of gas-recycling plants for maintaining reservoir pressures. In connection with the operation of such plants, it is particularly important to know how pressure and temperature will affect the yield of the liquid phase and the composition of the gas to be returned to the reservoir. It has not been possible to predict the behavior of these fluids that have high ratios off gas to liquid by comparing them with the behavior of low gas-liquid ratio fluids at identical pressures and temperatures. Such comparison fails because the proportions in which a component will be distributed between the phases of a system at any given temperature and pressure depend increasingly on the composition of the mixture as the critical temperature and. pressure of the system are approached. Because many combination wells are producing from reservoirs that have temperatures near the critical point, experimental date on the properties of the Fluids under reservoir conditions are particularly important at this time, To meet the immediate requirements of the industry for such experimental information, an equilibrium cell has been constructed at the Petroleum Experiment Station of the Bureau of Mines, Bartlesville, Okla. When adequate experimental date have been accumulated, it may be possible to make dependable estimates of the phase relations for high gas-liquid ratio fluids at the pressures anti temperatures characteristic of "combination-well? reservoirs.

Jan 1, 1940

By John A. Johnson

The first report of investigations5/ in this series pertaining to the investigation of stemming at the Mount Weather testing adit dealt with dust produced from blasting. The present report discussed the effect of stemming on eases generated by blasting, describes the test procedure, and analyzes the results from, blasting 61 standard rounds. Following care the types of stemming that are being investigated: 1, No stemming. 2. Sand in 2 paper cartridges. Clay in 2 paper cartridges. Commercial hydrated lira in 2 paper cartridges. 5. Combustible blasting plugs. 6. Ceramic is blasting plugs with clay in 2 paper cartridges.

Jan 1, 1940

By Donald E. Cummings

Measures appropriate for the control of the silicosis hazard in mining cannot be formulated precisely, but sufficient knowledge1-l9 has accumulated during the past quarter century to permit the suggestion of useful, though partly empirical, rules for its alleviation. The industrial hygienist today recognizes that the peril incurred by the inhalation of harmful dust is a function of two variable factors—the degree of harmful exposure and the specific susceptibility of the exposed individual to pulmonary injury. Control of the danger arising out of prolonged contact with pernicious airborne particulate matter is consequently best exercised by influencing both of these recognized variables. Obviously the problem has two broad aspects—one, medical; the other within the province of the engineer. I—Factors Comprising Degree of Individual Susceptibility Thorough investigations conducted among miners who have labored for years in the presence of recognized silicosis hazards usually reveal an impressive difference in the injury incurred by men whose exposure to dust has been nearly identical. After a quarter century underground, one individual is short of breath and incapacitated with miners' complaint, while a fellow workman suffers no pulmonary embarrassment and is in good health. Physicians ascribe this oft-observed difference in reaction to individual susceptibility and express a universal regret when they deplore the fate that chose to make the predisposed youth a miner rather than a farmer. To trust the health of miners to fate at the present time is even more unfortunate, because many of the factors that influence man's susceptibility to dust are known, and can be accurately determined by competent medical methods. Among the most important factors comprising susceptibility to injury by dust are the anatomical peculiarities of the individual's respiratory mechanism, his physiological response to the inhalation of dust, his previous dust, exposure, the existence of pulmonary infections or other pathological processes in his lungs, his age,

Jan 1, 1940