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By P. D. Southgate

VIBRATION, both ultrasonic and sonic, can affect the course of a variety of metallurgical processes. Reports of work on this subject have appeared at intervals over the last twenty years and a thorough review has been made by Hiedemann,' who gives a full list of references. It has been established that both refinement of structure and outgassing of the melt can be produced in most metals with sufficiently intense vibration. Many of the experiments in this field have been carried out using alloys of direct commercial interest in production- type casting equipment. Here a different approach is adopted, and simple binary alloys which exhibit different types of structure are used to facilitate examination of the effects produced under well-controlled conditions. Results from this kind of experiment should enable the basis of larger scale experiments with similar types of materials to be better substantiated. The alloys selected for this work are: 1) aluminum of 99.2 pct purity, the principal impurity being iron, near 0.4 pct; 2) A1-1.8 pct Fe, which is near eutectic composition; 3) A1-4 pct Fe—the second phase, of composition FeAl3, forms distinct acicular crystals; and 4) A1-12 pct Si—although this is of eutectic composition, the silicon normally appears in the form of large plates. Experimental Method There are three practicable methods by which acoustic vibration can be transferred to liquid metals: a) vibration of the whole of the container; b) electromagnetic induction; and c) insertion of a vibrating probe into the liquid. Method c is chosen here, and a frequency of 8 kc per sec is used. The end of the probe is electrically heated so that the metal near it will be the last to solidify. This ensures that vibration is transmitted directly to the liquid metal without passing through any solidifying and pasty intermediate region, which would attenuate acoustic waves severely. In addition, the heating prevents solid metal adhering to the probe, with consequent detuning. The transducer assembly is shown in Fig. 1. A stack of Permendur laminations 30 cm long acts as a half-wave vibrator and a winding along its length carries polarizing and energizing currents. It is joined by a half-wave coupling bar to a mild steel exponential horn, which tapers from 3.8 to 1.1 cm diam. A stainless steel stub 3 cm in length is welded on the free end. The assembly is supported by a plate located at the node of the coupling bar. Acoustic radiation losses are minimized by allowing the free end of the transducer to protrude above the surface of the cooling water. The exponential horn serves the function of matching the acoustic output impedance of the transducer to the radiation resistance of the probe into the melt. Electrical drive is provided by a 1 kw generator. Measurements of probe vibration amplitude during melt treatment are obtained from a gramophone pick-up with the needle attached to the wide end of the horn. This device is calibrated with a microscope before use. Liquid aluminum is very actively erosive and solution of materials with which the molten metal comes into contactcauses difficulties. Erosion of the probes in particular can be severe since it is greatly accelerated by the vibration. Tests of various acous-

Jan 1, 1958

By G. J. Ballmer

Trucks Are Valuable Auxiliary Haulage Units in Rail Pits For: ( I ) Making railroad grades (2) Establishing benches (3) Making new dropcuts

Jan 10, 1951

By H. W. Knott, M. H. Mueller, P. A. Beck

The rolling and recrystallization textures in 300°C rolled uranium sheet were investigated using a Geiger counter diffractometer with the modified Schulz reflection technique. Seven sections of sheet material were used in order to obtain sufficient data for quantitative pole figures by the reflection technique. A special integrating specimen table was used for obtaining and recording the data automatically. The rolling texture was described in terms of several "ideal orientations" in which the stronger orientations have either the (1103 or (010) poles in the vicinity of the rolling direction. The recrystallization texture of the sheet uranium was also described by several "ideal orientations" which are somewhat different, except in one case, than the as-rolled "ideal orientations." RESULTS of an X-ray study of the deformation texture in rolled uranium rods were reported by Harris' in which a concentration of (010) and (110) poles was found in the rolling direction. More recently Seymour," Mitchell 'and Rowland,3 and Adam and Stephenson4 reported results obtained on uranium sheet rolled under various conditions of tem- perature and amount of reduction. Since the results of Seymour as opposed to those of the two other groups of investigators are not in full agreement, it seemed justifiable to publish the present data, obtained concurrently with the previously mentioned investigations.'-' The results with rolled and re-crystallized uranium sheet were also included in the paper, since they appear to be more complete than the only previously published texture data on recrystallized sheeL3 In the present investigation great care was taken to maintain complete separation of the reflections from different crystal planes, even in cases where the 20 angles differed from each other by less than

Jan 1, 1956

By T. D. Ledyard

SIR WILLIAM LOGAN, our great geologist, predicted that Canada would become eventually one of the greatest iron-producing countries of the world. Although possessed of numberless deposits of iron-ore, we have not yet done much to verify this prediction. Causes can be found for our backwardness, the principal one being

Jan 1, 1891

By W. T. Nightingale

The three gas-producing "pools" discussed in this paper are in Sweet-water County, southwest Wyoming, and Moffat, County, northwest Colorado. Hiawatha, North Baxter Basin and South Baxter Basin gas fields became economically important in 1929 when a 330-mile gas line connected them with Salt Lake City, Ogden and towns en route. This development immediately focussed attention on the gas-producing fields and the efforts of the producing company to develop them in an orderly, economical manner. Several outstanding interests were acquired and working agreements made with others. Thus the interference of natural drainage areas was avoided, the pernicious practice of drilling direct

Jan 1, 1930

By W. D. Steele, S. D. Brady

THE Pittsburgh coal seam in West Virginia contains the largest coal reserves of any coal seam in that State and is, therefore, one of the most important seams, and attains mineable thickness and purity throughout that part of the seam extending from the Northern Panhandle to Monon¬galia Co. thence south and southwest across the state to Wayne Co. near Huntington. The Pittsburgh coal is also mineable in the Upper Potomac region but is now practically exhausted there. The total mineable areas of this coal amount to 2,165 sq miles and are estimated, by the West Virginia Geological Survey, to contain 13% billion net tons. The largest body of Pittsburgh coal outcrops on the western edge of West Virginia, along the Ohio river as far south as Moundsville, West Va., going under the river at that point and extending at various depths down the river as far as Wetzel Co. line where it thins out to such an extent that it has little practical value, and on the eastern edge this large body outcrops along the Monongahela River. The territory to be covered by this paper is the area known as the Northern. West Virginia District comprising Wetzel, Monongalia, Marion, Preston, Harrison, Doddridge, Taylor, Barbour, Upshur, Lewis, Gilmer, Braxton and Calhoun Counties, and is also known as Dist. 3 under the Bituminous Coal Act. This region was originally opened for commercial mining along and adjacent to the Monongahela River around 1852 when the Baltimore and Ohio Railroad was constructed to Fairmont. It has been extensively developed, first, in 188o (when the Monongahela River Railroad, now B. & O. R. R., was constructed) between Fairmont and Clarksburg, and later, in 1916, between Morgantown and Fairmont when the Monongahela Railway was constructed and placed in operation, this area furnishing the major portion of the production over the past years. With the mining out of a great deal of this territory adjacent to the Monongahela River considerable interest has been developed in the back acreage; and within the past few years a number of diamond core drill holes have been made in the back areas of Monongalia and Marion Counties. In this back area the oil and gas well drilling showed that the Pittsburgh coal seam was of mineable thickness and ranged in depth from 350 to 1,000 ft below the surface of the stream valleys but this drilling did not furnish any definite data as to its thickness and quality. ECONOMIC IMPORTANCE The Pittsburgh seam in Northern West Virginia is of primary importance as a coal resource not only because of its large reserves but because of its contributing a very large part of the coal used in this country for general steam uses. The Pittsburgh seam is a consistently thick seam, averaging 8 ft in thickness, with very easy grades underground, so it has always been

Jan 1, 1948

By Francisco Cadena

THE construction of Norris Dam, built by the Tennessee Valley Authority on the Clinch River, a tributary of the Tennessee River, involved the production of coarse and fine aggregate for approximately 1,000,000 cu. yd. of concrete. A hammer-mill plant for the manufacture of sand from quarried rock was indicated as the most economical method of providing this material. The abrasive character of the feed as compared to the average hammer-mill feed made it necessary to control operations rather ciosely, and this resulted in the accumulation of many data bearing on production and maintenance. This paper will deal only with three specific sets of data, accompanied by such general infor-mation as may be necessary to explain the conditions under which they were obtained and followed by discussions on the relation of silica content to hammer wear, comparative costs of slugger and stirrup hammers, and comparative costs of tool-steel and manganese-steel grate bars.

Jan 1, 1937

By R. P. Smith, L. S. Darken

FOR a high-purity iron-carbon alloy, the phases existing at equilibrium at temperatures slightly above the temperature of the metastable eutectoid are austenite and cementite (hyper-eutectoid) or austenite and ferrite (hypo-eutectoid) and those below the eutectoid temperature (carbdn content > 0.02 pct) are ferrite and cementite. Such an alloy, held in a carefully controlled and measured temperature gradient (about 1 cm per deg) which includes the eutectoid temperature, then quenched and examined metallographicall.y, provides a precise measure of the eutectoid temperature. The samples were hollow cylinders approximately 1.3 cm OD, 0.63 cm ID, and 2.5 cm long, which had been carburized to the desired carbon content at 1000°C with an appropriate hydrogen-methane mixture. In order to cool the samples to room temperature with a minimum change of carbon content and absence of cracks they were quenched in a Cerro Bend bath at 480°C, followed by a water quench to room temperature. Three cylinders were suspended in the furnace1 in a purified helium atmosphere, by a closed end, thin wall, silica tube which also served as a thermocouple well. The top and bottom cylinders served only as a means of making the temperature gradient along the center cylinder more uniform. The temperature was determined with a platinum-platinrhodium thermel calibrated by comparison with a thermel certified (* 0.5OC) by the National Bureau of Standards. After holding in the temperature gradient for 24 to 72 hr the samples were quenched in Cerro Bend at 480°C, followed by

Jan 1, 1960

By Albert J. Phillips

FOR the most part, recent changes in nonferrous physical metallurgy have been gradual and of a transition nature rather than abrupt modifications of existing methods. Development of new alloys containing vital constituents in what formerly would have been considered minute amounts has necessitated more precise control of metallurgical procedure than ever before. Realization of the remarkable effects of minute amounts of specific foreign elements in many alloys has brought about a revolutionary control in the selection of even the most commonplace raw materials. In addition, recognition of the widespread occurrence of precipitation hardness in metal systems, and the utilization of many of these, has emphasized not only the need for precise temperature control but also the necessity for considering the time factor in its effect upon properties in the treatment of most metals. These needs have caused the development and widespread installation of equipment that permits precision of control undreamed of a generation ago.

Jan 1, 1935

By AIME AIME

This section contains announcements of general interest to the members of the Institute, but not always of sufficient permanent value to warrant republication in the volumes of the Transactions.

Sep 1, 1906

By AIME AIME

COUNCIL.* PRESIDENT OF THE COUNCIL. D. W. BRUNTON DENVER, COLO. (Term expires February, 1910.) . VICE-PRESIDENTS OF THE COUNCIL. J. PARKE CHANNING NEW TORE, N. Y. FREDERICK W. DENTON PAINESDALE, MICH. JOHN B. FARISH DENVER, COLO. (Term expires February, 1910.) W. C. RALSTON SAN FRANCISCO, CAL. IV. L. SAUNDERS NEW TORE, N. Y. H. V. WIINCHELL ST. PAUL, MINN. (Term expires February, 1911.)

May 1, 1909

By William H. Breeding

The remarks that follow are based substantially on experience covering 45 years, 80% of which has been in placer work, rather than on a review of available literature. Most commercial placers have been deposited by the action of water. The richer and more- difficult-to-mine placers are those in the headwater areas where gradients are steepest. The most lucrative placers are generally in inter- mediate areas where volumes are greater, fewer boulders are present, and gradients are from 3% to 1-1/2%. The higher volume, lower grade placers are in the lower reaches of river systems where gradients are lower. Where gold-bearing rivers have discharged into the sea, wave action can concentrate values on beaches, past and present. Most of the rich, readily accessible placers were mined by our forefathers. Current opportunities exist: (1) in remote areas where infrastructure has been absent in the past, or development has been prohibited by adverse ownership - political or commercial; (2) in deposits that could not be mined by equipment available to our forefathers; (3) in deposits unidentified by our forefathers; (4) where the-price-of-product/cost ratio is substantially better than in earlier years; or (5) a combination of those factors. When I entered the placer business in the late 1930s, and subsequently, a prevailing opinion believed that glacial deposits should be avoided as irregular in mineral content and composition, and unrewarding to explore and develop; yet an operator has been mining a fluvio-glacial deposit profitably for the past 17 years. Rich buried placer channels, of ten called paleo-channels were worked in the last century, generally by hand methods, and under conditions that would be unacceptable today. Exploration and mining equipment now available make some of these channels attractive targets. Well-known examples are in California and Australia. The formation of a commercial placer requires a source of valuable minerals. Above primary deposits, there may be eluvial deposits formed by the erosion of gangue minerals and the concentration "in situ" of valuable minerals. Down slope from these deposits are the hillside or colluvial deposits, and below them are the alluvial deposits of redeposited material. Most of the great placer fields of the world are the result of several generations of erosion and deposition. Well-known examples are in California and Colombia. Gold is a very resistant and malleable material, and gold placers may extend for 64 or 80 km (40 or 50 miles) along a river system. Platinum is less malleable, but is very resistant to disintegration. Diamonds are extremely hard, and (especially gem diamonds) may be found over great lengths of a river system. Cassiterite is less resistant to disintegration, and tin placers seldom extend over two miles without resupply from an additional source or sources of mineralizaton. Tungsten minerals are generally more friable, and within a few hundred yards of the source disintegrate to the point that they are uneconomical to recover. Rutile, ilmenite and zircon placers generally result from the weathering of massive deposits, and may be encountered over extensive areas; most are fine grained and durable. What does a geologist or mining engineer look for in placer exploration? The old adage to look for a mine near an existing mine is still valid. You need a source of valuable mineral. Then you require conditions for concentration, which means a satisfactory gradient and/or other conditions that will permit heavy minerals to settle. Nicely riffled gravel, often called a shingling of the bars, is conducive to placer formation. Coarser gravel is logically associated with coarser gold. Excessive clay and/or high stream velocities in narrow channels can carry gold far downstream and distribute it uncommercially over a large area. When material is extremely fine, in situ weathering and concentration become more important. Placers frequently occur distant from lode mines, and one must remember that in a larger watershed the exceptional floods that occur once in a hundred or a thousand years can move great quantities of material long distances. The carrying power of water is said to vary with the fifth or sixth power of its velocity. I am not ready to disagree with Waldemar Lindgren and accept that many commercial placers are substantially enriched by the chemical deposition of gold from solutions; however, I have seen crystalline gold in clayey material quite distant from known sources of primary gold that is dif-

Jan 1, 1985

By D. C. Hilty, W. Crafts

L. S. Darken—Laboratory investigation of deoxidizing and other steelmaking reactions is usually centered, at least first, on the determination of the equilibrium or equilibria involved. This seems a reasonable procedure since equilibrium, if attained, depends only on composition, temperature, and pressure; hence conclusions derived from data on small experimental quantities are applicable to a heat of steel providing eauilibrium is attained in both cases. A knowledge of equilibrium serves as a useful framework even though we may know that practical conditions do not correspond to complete equilibrium. On the other hand, nonequilibrium or rate phenomena depend on a wider variety of conditions and are more difficult to interpret; conclusions applicable to laboratory conditions may or may not apply to larger scale phenomena. Hence the attainment or nonattainment of true equilibrium in the experiments here reported is of critical importance in evaluating their significance. Since some of the statements in this paper and in the closely related preceding one (on aluminum deoxidation) imply some doubt on this matter, I should first like to ask the authors whether their conditions are intended and believed to represent equilibrium. I should like to point out three considerations which seem to cast considerable doubt on the achievement of equilibrium, at least of the particular equilibrium under consideration. 1. In the experiments on manganese deoxidation the authors point out that they could not maintain the manganese-oxide slag on top of the metal in their rotating crucible, and hence they substantially dispensed with this slag. This leads to serious trouble in the interpretation of the results, for any equilibrium is, of course, a particular specific equilibrium—in this case Mn + O = MnO The experimental deletion of the upper layer of manganese oxide means that if equilibrium is attained at all it is attained between the metal and the MnO which has soaked into or adhered to the crucible (under the metal) and has dissolved substantial amounts of the crucible material including impurities. These impurities may constitute a significant portion of the slag by virtue of the small total amount of slag, even though the crucible is relatively pure. Hence there would seem to be a strong presumption that the equilibrium (if attained) involves not a pure MnO (or MnO — FeO) slag but one saturated with alumina and containing perhaps considerable impurities which substantially lower the concentration and activity of MnO, causing the above reaction to proceed to the right further than it would in the absence of alumina and impurities. Hence it is not surprising that manganese here appears as a better deoxidizer than found by other investigators. The present results may represent equilibrium with a slag of unknown composition which seems unlikely to be particularly related to plant experience. 2. The curves representing the observed silicon deoxidation (figs. 3, 4, and 5) are all drawn with a discontinuity in slope at about 0.02 pct oxygen. This point is interpreted as corresponding to the three-phase equilibrium, metal, slag, solid silica. The type of construction shown in these figures (though apparently fitting the data) is contrary to a fundamental principle of heterogeneous equilibrium as pertains to the construction of phase diagrams. According to this principle, the two solubility curves (each of the two portions of the curves in figs. 3, 4, and 5) must intersect in such manner that their (metastable) extensions must lie outside the homogeneous field rather than inside as in these figures. In other words, the "point" in these curves should be aimed in the opposite direction, if it is to be interpreted as corresponding to the three-phase equilibrium. The construction adopted is in violation of the second law of thermodynamics. This matter is discussed in detail in several texts and also by Lipson and Wilson.&apos;" The same criticism applies to the later figures representing conditions for manganese additions. The occurrence of this discontinuity or break at 0.02 pct oxygen casts further doubt on its interpretation. The earlier investigation of this system by Korber and Oelsen is in substantial agreement with the several recent findings of Chipman and coworkers that the oxygen content of iron in equilibrium with silica and silica-saturated iron oxide slag is about one third to one half that (0.24 pct at 1600") of iron saturated with pure iron oxide; thus there seems reliable evidence that iron saturated with silica and iron silicate slag at 1600" contains about 0.1 pct oxygen, or certainly much more than the 0.02 pct proposed in this paper. 3. In the quarternary system iron-silicon-manganese-oxygen one of the equilibria involved may be written 2 Mn + SiO2 (solid) = 2 MnO <slag> + Si The activity of SiO, is constant (if equilibrium is attained) by virtue of its presence as a substantially pure solid. At not too low metallic manganese content, the activity of MnO in the slag is constant by virtue of the fact that the slag is substantially pure manganese silicate saturated with silica and hence of constant composition. Thus the equilibrium constant for the above reaction is asi/a2Mn. Barring unanticipated large changes in the activity coefficients, the equilibrium constant may be adequately approximated for the composition range covered as [% Si]/[% Mn]2. Thus a plot of log [% Mn] against log [% Si] would be expected to be linear with a slope of one half as found by Kijrber and Oelsen. In the present investigation the slope (shown in fig. 15) is found to be one. It is difficult to believe that this finding represents a correct equilibrium determination, since it is at odds both with prior experimental investigation and with. theory. In view of the above points it seems that, although this paper reports many interesting findings, there is room for considerable skepticism as to the attainment of equilibrium and as to the conclusions drawn. N. A. Gokcen—The authors consider that Si% x O2% product is constant. This product is a function of the asi X a0 activity of Si02. The true constant is -------------. If the asio2 slags of this investigation were always saturated with SiO2 then Si% X O2% product would be constant,

Jan 1, 1951

Freeman, the English historian, said that he had learned from Macaulay "never to be afraid of using the same word or name over and over again if by that means anything could be added to clearness or force. Macaulay never goes. on, like some writers, talking about &apos; the former &apos; and &apos;the latter &apos;, &apos;he &apos;, &apos;she &apos;, &apos;it), and &apos;they’, through clause after clause, while his reader has to look back to see which of several persons it is that is so darkly referred to". He might have learned also from Macaulay that a preposition makes a feeble ending for a serious statement. How often do you hear &apos;the former&apos; and &apos;the latter&apos; in conversation? Good conversation is a guide not to be disdained. When you must use &apos;the latter &apos;, do not confuse it with &apos;the last &apos;. Cheap labor, cheap fuel, and cheap transport are essential, the latter [last] being particularly important in base-metal mining. The apparatus may be used to determine such gases as hydrogen sulphide, chlorine, oxides of nitrogen and some others, as well as sulphur dioxide. In the case of the latter two, etc. The two last mentioned are "sulphur dioxide" and "some others". He should have stated which two, and he should have avoided that wretched phrase "in the case of ". Pinning may be partly prevented by use of chalk, oil, or turpentine. The latter [last] is beat. "Partly prevented" is a poor phrase. &apos;Prevented&apos; is a word that does not lend itself readily to modification. He means &apos; checked &apos; or &apos;corrected &apos;. These steps are necessary to produce the gas, crude oil, and ammonia, the latter [last] of which is in solution in the water obtained along with the oil.

Jan 1, 1931

By Ernest Stütz

The problem of increasing blast-furnace efficiency through diminution of flue-dust production while operating with burdens consisting largely of fine ores has of recent years attracted the attention of metallurgists, whether directly or indirectly interested in the economies of iron smelting, and the various methods evolved from theory or practice have been submitted to wide discussion. After the very thorough and, at that time, exhaustive view of the whole subject, which was afforded to the industry by the meeting of this Institute in February, 1912, the subject was again taken up at the meeting of the Verein deutscher Eisenh?ttenleute at D?sseldorf in December, 1912. While American and German conditions are not entirely identical, it may be of interest to give here the words of the gentleman summing up the discussion at the Diisseldorf meeting: " The chief advantage offered by the use of briquettes lies in the fact that disturbances in the furnace, caused mostly by the presence of fine ores in the burden, are avoided, and that blast pressure can be considerably reduced. The resulting economies cannot be overrated, as, with lower blast consumption per ton of product, the installation will be able to take care of increased production. In consequence of lower pressure and speed of blast, heat is more efficiently utilized, flue gas temperature is lowered, and coke particles are less liable to be carried along with the flue dust, of which considerably less is produced. Finally, by increased regularity of operation and higher temperature in the lower parts of the furnace, the quality of the product is improved. The question of briquetting iron ores has grown to be one of the most important in the iron industry, and it is not any more a question of what is the cost of briquetting a ton of ore, but what, in using ore briquettes, is the cost of production of a ton of iron." Dr. A. Weiskopf, of Hannover, admirably condenses in these words

Jan 1, 1914

By William N. Page

HAVING recently made a careful professional examination of this tract, I think its peculiar geographical, topographical and geological relations may prove interesting to members, not only because they are somewhat unusual in such a combination, but also as presenting the economical conditions of a region not widely known, at the western base of the Alleghanies.

Jan 1, 1889

By M. M. Fine

In a laboratory study of grinding and classification of silica sand, a satisfactory means of producing the medium-fine specification sand desired by producers of flint-glass containers was developed. The best procedure consisted of ball-mill grinding and double classification, which gave a properly sized sand containing less iron than the feed.

Jan 3, 1950

By D. R. Weir, R. M. G. S. Berezowsky

Pressure oxidation of gold containing concentrates and ores is an effective pretreatment for liberating refractory gold. This is particularly true when an appreciable portion of the gold is associated with sulfides and is not amenable to conventional cyanidation. A brief review of the literature on pressure oxidation of refractory gold materials is presented. The chemistry of the aqueous oxidation of arsenopyrite and pyrite is discussed. Data obtained on pressure oxidation and subsequent cyanidation of concentrates and ores tested at the Sherritt Research Centre are also presented.

Jan 1, 1985

By F. C. Blake

The apparatus which I shall describe in this paper has been in ase for some time at the laboratory of the Pennsylvania Lead Company&apos;s works, and has been found to give good results, and to be simple and convenient. Steam Bath.—This steam bath is shown by Figs. 1, 2,3 and 4. It is made of sheet copper, about one-twelfth of an inch thick, the joints being brazed, and is used for heating the bottles in which the silver samples are dissolved,-previous to the fineness determina-

Jan 1, 1882

By P. G. Linder

The mechanical concentration of ores has not attained any considerable extent in Sweden, by reason of a scarcity of ores calling for this kind of treatment. Of rich iron-ores there is still an abundant supply; and magnetic concentration, which in the future undoubtedly will become of great importance, not being as yet demanded by necessity, has not advanced beyond a few experiments. At the copper-mines mechanical concentration has been superseded by chemical processes; the lead mines are worked out; and it is (with one exception) only the mines producing blende, or blende and galena intimately mixed, that have adopted mechanical methods for enriching their low-grade ores. While the concentrating-plants in Sweden are few and their output is comparatively insignificant, the methods employed, the general features of the work and the results obtained under extremely unfavorable conditions, may offer some points of interest to persons who are engaged in this branch of industry and have similar problems to deal with. Before going into a detailed description of the several plants, I will offer a few remarks that hold good for all of them and constitute a general review of Swedish concentration and its conditions. At all the works the ore to be treated is a mixture of blende and

Jan 1, 1895