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By P. Barnes

THE complete and accurate filtration of water (if the word ,accurate may be thus used) for the feeding of boilers, and for many similar industrial purposes, although somewhat practiced both at home and abroad, has been by no means common. Even if the exact line cannot be defined at which filtration begins to be called for, and will be found profitable, it is certain that in a large number of cases it may be employed with real advantage in the economy of fuel, and also in. the greater durability of the boiler or other form of apparatus in

Jan 1, 1882

By Jon Kogut

This paper describes three programs, currently in use within MSHA, for graphic analysis of accident frequency data. The first program, TREND, plots confidence bands for curved trends in data compiled over a period of time. In addition to detecting statistically significant upward or downward trends, the program can be used to determine whether an observation at a particular time deviates significantly from the historical pattern. The second program, POIPORP, plots interval estimates for the risk of accident in each of several environments, given an observed number of incidents and exposure time at each environment. POIPORP is designed to quantify the uncertainty implicit in incidence rates based on limited information and to facilitate statistically valid comparisons among the rates. The third program, CINDY, plots dynamically adaptive control charts for accident or injury experience at a given location. These charts are used to detect statistically significant departures from a changing standard or a previously established trend. All three programs are written in FORTRAN IV, utilizing DISSPLA and IMSL. They exemplify forms of statistical analysis that would not be practical without a computer. Use of the programs is illustrated with applications to coal mine fatality and injury experience.

Jan 1, 1983

By Tadao Nagai, Masao Sato

Electrochemical measurements have been carried out in an auto- clave to investigate the electrochemistry of hydrogen precipitation of nickel from acetate buffered solution. After having previously obtained the rate equation for this reaction we have now made a concentrated effort to explain the rate equation electrochemically. A saturated NaC1-type Ag/AgC1 reference electrode has been improved so that it can be used in an autoclave. Polarization curves for the reaction, [H2=2H+ + 2e,] on nickel electrode were measured in solutions free from nickel ions at 185°C, and the parallel curves were obtained by changing PH2 and pH for normal and reverse reactions, respectively. Polarization curves in nickel solutions were complex, probably because the potential of hydrogen electrode is close to that of nickel and of the nickel surface altered during polarization. Then the nickel electrode potential and the reaction rate were measured simultaneously during pressure reduction at various hydrogen pressures and at various nickel concentrations. The reaction rates in terms of current density were plotted to obtain the local polarization curves for reactions Ni2+ + 2e ? Ni and H2 ?2H+ + 2e. The anodic and cathodic local polarization curves exhibit potential dependency. Therefore it is likely that the pres- sure reduction can be regarded as a coupled electrodes reaction.

Jan 1, 1973

By B. J. Kochanowsky

The primary use of a portable crusher, i.e., a crusher mounted on crawlers or tires, in the rock and mining industries is to reduce costs by permitting the substitution of conveyor belt haulage for truck or track haulage. The usual sequence of operations in surface mining is drilling, blasting, loading, haulage, and crushing. Haulage is normally accomplished by truck or track-mounted cars, the latter method being used for the longer distances. However, by using a portable crusher in the pit, the sequence of operations would be changed so that the crushing stage would occur before haulage (Fig. 1). Such a sequence would permit the use of conveyors to replace the more expensive truck or track haulage methods. Since most quarry and open pit operations normally require a crushing stage, the only additional costs incurred will be due to the investment required to purchase or construct a mobile arrangement for a crusher. But this factor has to be weighed against the advantages to be gained by conveyor haulage. As shown in Fig. 2, transportation of material by belt conveyor over short distances is less ex- pensive than by truck. The inclination of the belt has no effect on belt speed; consequently, the hourly tonnage moved remains the same. Conversely, the output rate of trucks as expressed in tons or ton- miles per shift decreases proportionally to the haulage speed, which is considerably slowed by the steepness of the road (Fig. 3a). Although maximum possible grades and maximum economic grades of haulage are greater for a belt than for a truck (over the same total lift), the longer haulage distances favor the use of trucks.

Jan 12, 1960

By S. K. Kawatra

The paper describes a system for on-line analysis of ash in solids in coal slurries for coal cleaning operations. The system consists of two sensors: 1) gama density gauge, and 2) ash sensor. The operational characteristics of each sensor are discussed.

Jan 1, 1980

By R. E. J. Putman

Introduction Self-tuning regulators are a class of controllers built around the concepts of sampled data theory, and are especially suitable for implementation in a digital microprocessor or minicomputer control system. The algorithms used are distinctly different from those based upon analog control techniques and include automatic adjustment features which permit them to adapt to unmeasured changes (in, for example, ore grindability) or process nonlinearities (as exhibited by cyclone classifiers). They are also designed to handle transport lags in a simple manner, for example, anticipating the effects of a variable recycle rate on particle size distribution. The advent of distributed control systems will encourage the exploration of these techniques in the minerals processing industries, and particularly for improving the control of comminution circuits, which are especially energy intensive. This paper outlines some current work in progress on this topic. Background Those engaged in the practice of process control have long had two philosophical problems for which solutions have been actively sought - what is optimal control and how can we attain it in some heuristic fashion automatically. The basic analog controller can be represented by the differential equation: [V = Ko + K1 f y • dt + K2 dt(1)] where: v and y are the instantaneous values of output and error respectively and K0, K1, and K2 are tuning constants. The empirical rules for establishing the values of K0, K1, and K2, which provide stability, have evolved from the initial suggestions of Ziegler and Nichols(9) in 1942 and have served their purpose well. However, later analyses demonstrated that there are in fact many combinations of the values of K0, K1, and K2 which, besides being stable, behave better or worse in relation to other process control criteria; some examples are duration of error, amplitude of a damped response, magnitude or rate of movement of control valve or adjustment of speed regulator, etc. The definition of optimality had broadened. In 1964, Kalman(4) published his classic paper which tried to resolve these problems. He defined a

Jan 1, 1982

J. C. WRIGHT.-The problem of organizing and maintaining a vocational class for those employees who are engaged in the mining industry depends on several most important factors. The first is the sympathetic cooperation of employer and employee; the second is to find the subject matter that must be presented to these men; and the third is to find the instructor who can present that subject matter. This is perhaps the most difficult, for we usually find a man who knows the material that is to be presented but is not a teacher or does not know how to organize his material. The man must know the subject matter from the standpoint of absolute contact with industry in order to be a successful teacher. I have come into contact with two kinds of schools organized in connection with mining occupations. In one type the instruction leans very largely toward elementary subjects, arithmetic, reading and writing and spelling; it is not of such a character as to help or improve the working man in his occupation in the sense that we are attempting when we speak of vocational education. In the other type of school, an engineer is usually employed as a teacher. He immediately begins to give the things with which he is most familiar and the instruction becomes such as only those who possess a high-school or college education, perhaps, are able to receive. In between these two schools is the school we are trying to, promote, a school that will meet the needs of those employed. MARGUERITE W. JORDAN,* Altoona, Pa. -Vocational education has become the business man's problem; for he is the keeper of that white elephant, labor turnover, and anything that will decrease the size of the monster is worthy of serious consideration. This vocational education can do; for it can supply many of those deficiencies in upbringing and. environment that make for the discontent and restlessness of our varied classes of unskilled labor: the Anglo-Saxon mountaineer; the Southern negroes who have crossed Mason & Dixon's line by the thousands, "searching satisfaction for our minds;" and the still greater number who have sought across the sea America, "the promised land.

Jan 4, 1919

By Mark R. Lamb

The recent growth of a sentiment among cyanide-plant designers against the use of gravity-stamps for the crushing preliminary to cyanidation may be said to date from the almost simultaneous perfection of the ribbed tube-rnill liner and of the tall, air-agitation tank. The first step in the resulting change of practice mas the universal adoption of the tube-mill for fine-grinding and the use of coarse screening on the battery. This was the beginning of the surrender of supremacy by the gravity-stamp; since merely the single fact that it was a more economical machine for crushing fine had retained it in favor as conlpared with ball-mills, rolls, or steam-stamps. The surrender, however, is not yet complete.

Jan 1, 1911

By Charles J. Speake, Dennis R. Haley, Thomas E. Finch

The tremendous interest in development of surface- mineable coal throughout the western US will bring with it a requirement for many manhours spent in mine planning and equipment selection. One problem in particular that engineers face during the planning stage is that of selecting a dragline with the proper reach capability. Reach, expressed in terms of operating radius and effective spoil radius, can be a major problem when mining deeper than originally planned, and aside from production requirements, the ability of a particular dragline to spoil across a strip is essential. Determination of dragline reach needed for a multiple-seam western coal operation can be simplified by use of an equation derived below that eliminates the need for tedious and repetitive calculations.

Jan 5, 1977

By C. A. Heiland

THE Eötvös torsion balance permits the measurement of certain second derivatives of the gravity-potential, which are known as the gradients of gravity and the curvature values for an, equipotential plane of gravity. These quantities are influenced on level ground by the configuration of the masses underneath. Hence, the torsion balance has gained great importance for the location of geological structures and thus indirectly for the discovery of oil and other mineral deposits. If the ground is not level, however, the measurements become more difficult, because the superficial mass-irregularities also produce more or less considerable disturbances. It is necessary, therefore, to determine the shape of the surrounding topography by leveling as well as by consulting topographic maps and to compute its influence upon the torsion balance. The correction thus determined is called, in general, the topographic correction; it is composed of two constituents, the terrain correction and the cartographic correction. The terrain correction would be that part of the topographic correction as derived from the direct leveling of the area surrounding the station, whereas the data for the computation of the cartographic correction are obtained from a topographic map, usually beginning with a radius of 100 meters, as under most circumstances it is difficult to level along a larger concentric circle about the station.

Jan 1, 1928

By C. A. Heiland

THE Eötvös torsion balance permits the measurement of certain second derivatives of the gravity-potential, which are known as the gradients of gravity and the curvature values for an equipotential plane of gravity. These quantities are influenced on level ground by the configuration of the masses underneath. Hence, the torsion balance has gained great importance for the location of geological structures and thus indirectly for the discovery of oil and other mineral deposits. If the ground is not level, however, the measurements become more difficult, because the superficial mass-irregularities also produce more or less considerable disturbances. It is necessary, therefore, to determine the shape of the surrounding topography by leveling as well as by consulting topographic maps and to compute its influence upon the torsion balance. The correction thus determined is called, in general, the topographic correction; it is composed of two constituents, the terrain correction and the cartographic correction. The terrain correction would be that part of the topographic correction as derived from the direct leveling of the area surrounding the station; whereas the data for the computation of the cartographic correction are obtained from a topographic map, usually beginning with a radius of 100 meters, as under most circumstances it is difficult to level along a larger concentric circle about the station.

Jan 1, 1928

By Bension Varon

Systematic projections of mineral supply, demand and prices are an integral part of the mineral sector planning process. As such, their primary value is not as prophecies but as devices for imposing discipline on thinking about the future and as means of ensuring consistency in policy decisions. Both the present and the broad outline of the future as presently discernable affect projections on specific minerals. The present world mineral situation reflects most prominantly the recent commodity cycle while our view of the future is largely shaped by perceptions and attitudes of policy-makers and the public over larger issues. Mineral commodities are of considerable importance to various countries. This in itself dictates a strong interest in systematic projection activities, the need for which is heightened by the volatility of certain basic variables affecting mineral demand in the world. It is useful for presentation purposes to discuss the various techniques suited for projecting mineral trends under three principal headings, viz., econometric modeling, systems analysis and technological forecasting. In addition, two specialized variants, input-output analysis and resource base modeling, are discussed. In each case, a brief description of the approach and some indication of its application to projections of mineral commodities are provided.

Jan 1, 1977

By Erwin Zodrow, De Verle P. Harris

The Smallwood mine, owned and operated by the Iron Ore Co. of Canada, is one of the largest ore producers in Canada, producing about 15 million tons of crude ore per year. Located in the Labrador Trough near, Labrador City, Newfoundland, the open-pit operation has ore consisting chiefly of specular-hematite, with some magnetite. The magnetite content of the ore as a mineral percentage is small, but it is of considerable importance in ore grading because of its effect upon milling. Being harder than specular-hematite, magnetite increases grinding time and milling costs. Specifically, higher grade magnetite (greater than 15%) usually occurs as fine grains in a fine grained siliceous rock matrix (also as larger octahedra in carbonate bands). This tends to increase the overall breaking strength in the crude ore; consequently, the hourly mill rate and the weight recovery decrease. At the same time, because of its relatively high iron content, the magnetite does contribute to the amount of iron in a block of ore. Were the concentration of the magnetite relatively constant, its presence would be of less consequence, for appropriate adjustments could be made in the milling operations. However, the quantity of magnetite present for any run of ore varies considerably; it is the magnetite prediction for a block of ore that constitutes the greatest problem in grading. THE PRESENT ORE GRADING METHOD Ore for the Smallwood mine is graded by a computerized block grading routine (using 50 x 50 x 45-ft blocks) that applies simple weighted (inverse-distance) averaging to ore grades. The results of the block grading program are not reliable with respect to magnetite concentration. Factors responsible for this poor estimation are (1) the structural setting of the deposit, and (2) mineralogical relationships. Neither of these general factors are given adequate consideration by present methods.

Jan 8, 1967

By Jose A. Ruiz

INTRODUCTION For heterogeneous non-catalytic solid-gas reactions carried out in fluidized bed reactors, nominal bed temperature is an average value between gas and solid. For highly exothermic reactions, actual particle temperature can be up to hundred degrees above termocouple temperature, since heat dissipate at slower rate than heat generation during some steps of transformation. These micro instabilities at particle level can displace thermodynamic equilibrium from the desired phase to others. This effect is important when relatively narrow range of phase stability exists, like in sulphation roasting of sulphides, where bed discharge contains, in addition to the desired sulphate others metastable phases such as basic sulphate and ferrite. For example, for copper-iron sulphide concentration roasted below 680°C, no cupric ferrite is formed, as shown by Jakob et al., therefore the separate Kellogg's stability phase diagrams Cu-S-O represent the roasting (Fig.l). At temperature above this one, like 760°C for example, phase stability changes from CuSO4 to the basic sulphate Cu0•CuSO4. Solid state reaction between Cu0•CuSO4 and Fe203 also occurs to form cupric ferrite, Cu0•Fe2O3, therefore the Cu-Fe-S-O Kellogg's phase diagram of Fig. 1 (continuous line) represents this condition of roasting. Although both Cu0•CuSO4 and Cu0•Fe2O3 are metastable phases under normal operating conditions of sulphation roasting(1-10% SO2, 1-10% 02 and 680°C, points A and B,Fig. 1) sulphation of these species and particularly ferrite are slow and limited due to diffusional control. This explain why reactors discharge contains several phases: CuSO4, Cu0•CuSO4, CuO•Fe203 plus small amounts of CuS and FeS due to the baclonixed conditions of fluidized bed reactors. The presence of cuprous ferrite due to reducing conditions inside individual particles also occurs, but in very limited extent at the reaction interface, as it is demonstrated by the low soluble iron levels of calcines. On the other hand, the presence of cupric ferrites can be explained only due to the higher temperature achieved by particles, since below 680°C cupric ferrite formation does not take place. [ ] This phenomena also occurs for others non-ferrous metal sulphides concentrates roasted under sulphation conditions, such as 7n, Co and Ni. Therefore the prediction of discharge composition of fluidized beds is not possible based only on kinetics and mechanistics models alone or purely thermodynamical considerations, since all factors should be integrated to describe the overall phenomena. SINGLE PARTICLE TRANSFORMATION Assuming a first order reaction with respect to the gas and zero for solid, such as

Jan 1, 1984

These pages may be used as order sheets. Mark the number desired opposite title of pamphlet wanted, add your name and address, tear out the sheets and mail them to us. Single orders 25 c. Pamphlets 10 c. each in lots of three or more. Pamphlets 5 c. each in lots of fifty or more. These prices prevail for orders for pamphlets of the same or different titles, when cash accompanies order. The pamphlets listed on the following sheets are advance copies printed to facilitate discussion at the meetings of the Institute. They are offered for sale at the reduced prices given above as long as the supply lasts. This list is published in the Bulletin in order that members may have the first opportunity to secure pamphlets, which sometimes are in such great demand that the supply is exhausted before the wants of members can be supplied. The following list includes only a fraction of the pamphlets that have been published by the Institute. Any other paper published by the Institute may be obtained for the price of $1, except those published in Volume XXXI, which are rare. The Institute is still selling back volumes of Transactions at reduced prices, but some of these volumes are becoming rare and members who desire to complete their sets of these very important books on mining and metallurgy are advised to send in their orders as soon as convenient. The attention of members is also called to the bibliographical index of the science of ore deposits contained in the Emmons Volume which is selling at $3 in paper and $4 in half morocco. The Posepny Volume is already exhausted and members who do not get in their orders for the Emmons Volume at the present reduced price may soon find themselves unable to obtain it on such favorable terms.

Jan 8, 1917

These pages may be used as order sheets. Mark the number desired opposite title of pamphlet wanted, add your name and address, tear out the sheets and mail them to us. Single orders 25 c. Pamphlets 10 c. each in lots of three or more. Pamphlets 5 c. each in lots of fifty or more. These prices prevail for orders for pamphlets of the same or different titles, when cash accompanies order. The pamphlets listed on the following sheets are advance copies printed to facilitate discussion at the meetings of the Institute. They are offered for sale at the reduced prices given above as long, as the supply lasts. This list is published in the Bulletin in order that members may have the first opportunity to secure pamphlets, which sometimes are in such great demand that the supply is exhausted before the wants of members can be supplied. The following list includes only a fraction of the pamphlets-that have been published by the Institute. Any other paper published by. the Institute may be obtained for the price of $1, except those published in Volume XXXI, which are rare. The, Institute is still selling back volumes of Transactions at reduced prices, but some of these volumes are becoming rare. and members who desire to complete their sets of these very important books on mining and metallurgy are advised to send in their orders as soon as convenient. The attention of members is also called to the bibliographical index of the science of ore deposits contained in the Emmons Volume which is selling at $3 in paper and $4 in half morocco. The Posepny Volume is already exhausted and members who do not get in their orders for the Emmons Volume at the present reduced price may soon find themselves unable to obtain it on such favorable terms.

Jan 7, 1917

These pages may be used as order sheets. Mark the number desired opposite title of pamphlet wanted, add your name and address, tear out the sheets and mail them to us. Single orders 25 c. Pamphlets 10 c. each in lots of three or more. Pamphlets 5 c. each in lots of fifty or more. These prices prevail for orders for pamphlets of the same or different titles, when cash accompanies order. The pamphlets listed on the following sheets are advance copies printed to facilitate discussion at the meetings of the Institute. They are offered for sale at the reduced prices given above as long as-the supply lasts. This list is published in the Bulletin in order that members may have the first opportunity to secure pamphlets, which sometimes are in such great demand that the supply is exhausted before the wants of members can be supplied. The following list includes only a fraction of the pamphlets that have been published by the Institute. Any other paper published by the Institute may be obtained for the price of $1, except those published in Volume XXXI, which are rare. The Institute is still selling back volumes of Transactions at reduced prices, but some of these volumes are becoming rare and members who desire to complete their sets of these very important books on mining and metallurgy are advised to send in their orders as soon as convenient. (See Advertising page 15.) , The attention of members is also called to the bibliographical index of the science of ore, deposits contained in the Emmons Volume which is selling at $3 in paper and $4 in half morocco. The Posepny Volume is already exhausted and members who do not get in their orders for the Emmons Volume at the present reduced price may soon find themselves unable to obtain it on such favorable terms.

Jan 6, 1917

By S. Luszcz, R. W. Vook, Fred Witt

In situ X-ray investigations were made on polycrys-talline silver films deposited by vacuum evaporation on (111) CaF2 and (100) NaCl single-crystal substrates at 80°K. The films were evaporated and annealed in an X-ray diffractometer attachment having a residual gas pressure of 2 x lo-' Torr. All measurements were made without exposing the films to the atmosphere. Measurements were made on the films in the as-deposited state and after various annealing treatments. The intrinsic stacking and twin fault densities, the magnitudes of the uniform and nonuniform strains, and the crystallite sizes were determined. In addition the textures in the films were measured qualitatively. The results obtained for the as-deposited films on single-crystal substrates are in substantial agreement with previously reported results for silver films deposited on glass. Intrinsic stacking and twin faults, as well as uniform and nonuniform strains, were present in these films. During the various annealing treatments (up to 350°C) the faults and nonuniform strains annealed out. Considerable grain growth and texture changes occurred also. The effects were much greater for the NaCl substrate than for the CaFz substrate. The relative magnitudes of the grain growth in the variously oriented grains could be explained qualitatively in terms of the thermal strains and strain energies introduced into the differently oriented grains during the initial, irreversible anneal. These strains were due to the different thermal expansion coefficients of the film and substrate. X-RAY diffraction measurements on evaporated films deposited on substrates at low temperature have the advantage that many of the imperfections introduced into the film during deposition are "frozen in". Thus, the influence of a very important experimental variable, substrate temperature, on the imperfection structure of evaporated metal films may be studied. Moreover, the effects of annealing such films makes possible the study of thermally activated recovery processes in these films. The present study was designed to determine the influence of single-crystal substrates on the resultant film structure relative to the previous results obtained using glass substrates.' To this end great care was taken to keep the experimental variables the same in the two cases. Different experimental conditions would, of course, result in films having different physical properties. Again the initial substrate temperature was in the neighborhood of 80°K and the films were subsequently annealed to 350°C. The pure metal silver was chosen for evaporation, primarily because of its relatively low stacking fault energy and consequent high fault density in the as-deposited state. The silver films were formed by evaporation onto air-cleaved {ill} CaF, and (100) NaCl surfaces cooled to 80°K in an X-ray diffractometer attachment2 having a base residual gas pressure of 2 X l0-' Torr. The films were not exposed to the atmosphere until all of the X-ray data had been recorded. In this way one of the most important experimental variables, environment, could be well-controlled and reproduced. X-ray measurements were made at the temperature of deposition and included determinations of the diffraction line peak positions, line shapes, and integrated intensities. The peak position measurements were used to determine the intrinsic stacking fault densities and the average uniform strain in the film. The shapes of the diffraction lines provided information on the twin fault density, true crystallite size, and average nonuniform strain. The preferred orientation in the film was determined qualitatively from the integrated intensities. I) EXPERIMENTAL PROCEDURE The evaporator attachmentZ was charged with 99.999 pct Ag pellets positioned in a tantalum filament which had been outgassed previously at l0-8 Torr. The CaFz and NaCl single crystals were cleaved in air and then placed in position in the chamber so that their cleavage surfaces were on the diffractometer axis. The chamber was prepumped using a sorption pump, sealed off, and then baked at 150°C for 24 hr. The ion pump operated during the bakeout cycle. The substrate was then heated to 500° C by means of an auxiliary heater and kept hot until the rest of the chamber was cooled slowly to room temperature. This bakeout procedure consistently resulted in an ultimate pressure in the low lo-' Torr range. The substrate was then cooled down on 80°K. Its temperature was monitored by a thermocouple wedged into the rear of the copper substrate holder. The diffracted intensity and peak position of the 111, 222, and 333 CaF, lines were measured prior to evaporation. Nickel-filtered, pulse-height-discriminated copper radiation was used. Similar measurements were made for the 200 and 400 lines from NaC1. These measurements were used as a lattice parameter check and to determine the thickness of the evaporated silver films from the attenuation of the substrate lines. The evaporation rates were approximately 3A per sec for both films while the maximum pressures during evaporation were 3 x lo- ' and 7 x 10"8 Torr for the CaF, and NaCl cases, respectively. The film thickness was measured by the attenuation of the CaF, and NaCl substrate lines and by at optical interference method. Values of 1700 and 1500A, respectively, were obtained for the silver

Jan 1, 1969

By Paul Merica

ONE of the most useful, and at the same time least commonly used, methods of thermal analysis for the determination of transformations in metals and alloys consists in the recording of the tune intervals required for successive increments of temperature change during heating or cooling, the temperature of the furnace containing the specimen being altered at a uniform rate. The curve obtained by plotting these time intervals as a function of the mean temperature of the specimen during the interval is called the inverse-rate curve. It is probably due to the fact that no simple and convenient method has apparently been available for the measurement of the successive time intervals that this method has not been so generally used as, for example, the differential method, for which several tykes of automatic or semi-automatic apparatus have been designed. Whenever this method has been used, the intervals have usually been measured with the use of a chronograph; its operation as practised at the Bureau of Standards' is as follows: The temperature of the specimen is measured by a thermocouple and a dial potentiometer. The operator sets the potentiometer at successive values of the electromotive force differing by equal increments, usually 0.02 millivolt, and records the exact instant on the chronograph, by pressing a contact key, at which the galvanometer coil passes through its null position. Two-second intervals are also recorded on the chronograph record, and the number of 'seconds elapsing between successive signals is afterward counted from the record and plotted as a function of the electromotive force or of the temperature. This is an admirable method and by it most minute thermal arrests may be detected, but it requires a good chronograph, which is generally difficult to obtain, and the time of one operator during the recording and, subsequently, to read the intervals from the record; the latter operation often takes from one to two hours.

Jan 7, 1919

The following paragraph of appreciation of the Engineering Societies Employment Bureau is from the letter of a young engineer who found the Bureau of service. "I wish to sincerely thank you for the services rendered. They are of immense value to anyone located as I am, in a small town without the opportunities for keeping in touch with openings in manufacturing lines."

Jan 12, 1919