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By F. F. Peng, A. D. Walters, M. R. Geer, J. W. Leonard

INTRODUCTION Washability characteristics derived from float-and-sink analysis in Chapter 4 demonstrate that coal is intrinsically heterogeneous, and this heterogeneity is also evident in the proximate, ultimate, and size analyses. A range of particles from high to low specific gravity is usually seen in the run-of-mine coal. One objective of coal preparation is to recover the high quality float material (the particles of lower specific gravity) such that the recovered product meets certain quality specifications, as well as to reject or recycle low quality particles of higher specific gravity. The maximum recovery of cleaned coal at the required quality is of major concern to plant operators. However, the quantity and quality of products of coal cleaning, determined in the operation of actual commercial cleaning plants and by theoretical calculation based on run-of-mine washability studies, are known to be different with each coal. Therefore, during the last half century, coal preparation engineers have repeatedly sought methods to predict the technical and economical efficiency of separation of cleaning equipment and systems. Many formulas have been proposed by international investigators to evaluate the efficiency of various coal cleaning operations, primarily based on the yield and/or ash of the various products of coal cleaning. Performance criteria in use today are capable of defining all of the important aspects of a given concentrating operation; however each criterion has certain restrictions or limitations. It is important, therefore, to understand how such formulas can be used and the problems involved in their construction. Technical Measure of Plant Performance Conventional means for evaluating a preparation plant's performance are generally approached through the use of equipment performance mea-

Jan 1, 1979

By E. J. Kenaedy, E. H. Robie

THOUGH the fall meeting of the Coal Division was held in the heart of the anthracite section, at Hazleton, Pa., the bituminous industry was well represented also, and the two groups found much common ground for discussion. The' technical part of the program was confined to two sessions in the morning and afternoon of the first day, Friday, Oct. 14, the evening and the following day being reserved for field trips and social functions. The attendance more than met the expectations of those in charge of the arrangements; there seemed no hint of depression here.

Jan 1, 1932

By F. H. Ellinger

TI HE crystal structure of neodymium has been re-A ported by Quill1 and by Klemm and Bommer"s to be hexagonal-close-packed, Strukturbericht-type A3, with a, = 3.650.4, c, = 5.890.4, c/a = 1.614. Klemm and Bommer,% owever, pointed out that the observed intensities of the lines of the neodymium powder pattern agreed only in part with the intensities calculated for the type A3 structure, and that the neodymium powder pattern showed extra lines which could not be traced to impurities. They found that these extra lines could be accounted for by doubling the c-axis, but apparently they did not consider their evidence to be sufficiently conclusive to justify reporting the doubled c-axis. In the present work, the structure of neodymium was found to be double hexagonal-close-packed. The neodymium metal used in the present investigation was obtained through the courtesy of F. H. Spedding of the Ames Laboratory. Its major impurity was stated to be 0.03 pct Ca. The author's spectrographic analysis indicated high purity and carbon was determined to be less than 30 ppm. X-ray powder specimens were prepared from filings stress relieved in vacuum at 200°C for 50 hr. Powder photographs were taken in an 114.6 mm diam camera (Straumanis film mounting) at room temperature and in a 19 cm diam Unicam high temperature camera at elevated temperatures. Copper x-radia-tion was used for all the photographs. The powder pattern of neodymium was found to index to a hexagonal unit cell with dimensions, as determined from the high angle Ka doublets, of: a.= 3.655+0.001.4; c, = 11.796+0.004.4; and c/a = 3.227 at room temperature. The measured density of neodymium shows that this cell contains 4 atoms, the calculated density is accordingly D, = 7.02 g per cu cm. The diffraction data for the first 15 lines of the powder pattern are listed in Table I. In a double hexagonal-close-packed unit cell, the 4 atoms would be in the positions (0,0,0), (0,0,%), (1/3, 2/3, 1/4), and (2/3,1/3,%) of space group P 6,/mmc. On the basis of these positions, the relative intensities of the reflections were calculated using the expression: 1+cos2 20 I oc \Frp 1 ' sin2 0 cos 0 where F is the structure factor and p is the multi- plicity factor. Since absorption was not taken into consideration, comparison of observed and calculated intensities should be made only for neighboring reflections. Each atom has 12 neighbors, 6 in the basal plane at a distance of 3.655.4 and 3 above and 3 below at the closer distance of 3.626.4. These distances correspond to an average radius of the neodymium atom of 1.820.4. The description of this structure in terms of A, B, and C close-packed layers of atoms is ABAC ABAC. ...... The structure repeats every fourth layer and the stacking sequence of the second, third, and fourth layers corresponds to cubic-close-packing of atoms. A series of powder photographs taken at successively increasing temperatures up to 680a10"C revealed that the double hexagonal-close-packed structure is stable up to this temperature. Acknowledgments The authw wishes to thank W. H. Zachariasen and A. S. Coffinberry for their helpful comments on this work and also Marion Gibbs for measuring the diffraction films. This work was sponsored by the United States Atomic Energy Commission.

Jan 1, 1956

By R. E. Sinke

Demerara Bauxite Co. in British Guiana has come a long way in tackling the problem of stripping and removing overburden. When the company started mining in 1917, overburden was hand-loaded into carts pulled by donkeys. Since then it has been recognized that overburden removal is one of the greatest problems. Over the past years a great quantity of equipment has been purchased, discarded as it became obsolete, and replaced with better and cheaper tools. The policy has kept the company's overburden removal costs within reason. Accurate records of costs per cubic yard and cubic yards per hour per unit have been kept for many kinds of equipment. Walking draglines and hydraulicking equipment are the key approaches to the current operation, but shovels, tractor-drawn wagons, self-propelled rubber tired scrapers, and tractor-scrapers still have limited applications. Mackenzie, operational headquarters of the Demerara Bauxite Co. Ltd., is on the Demerara River, 65 miles from Georgetown, British Guiana. Ore treatment and ship loading facilities are at Mackenzie, head of navigation for ocean-going vessels and the mines are located 7 to 40 miles farther upstream.

Jan 4, 1955

(Under this heading will be published notes sent to the Secretary of the Institute by members or other persons introduced by members.) Member, also Assoc. Mem. Am. Soc. of C. E.; excellent technical education, and best of references covering 12 years in responsible charge of work; experienced in surveys, construction, prospecting, mine

Jan 12, 1917

By H. M. Fisher, R. E. Snow, S. C. Sun

RAPID colorimetric estimation of the amount of transparent minerals has been applied success- fully to instream mill products at the cryolite flotation plant of the Pennsylvania Salt Mfg. Co., Natrona, Pa. Apparatus used was a Bausch & Lomb monochromatic colorimeter. The optical assembly of the colorimeter, shown in Fig. 1, passes light from a 6-v, 32-cp, prefocus incandescent lamp through two condensing lenses, a heat-absorbing filter, an aperture-control diaphragm, an interference filter, and a sample container. The light finally strikes a barrier-layer photocell and the output current of the photocell is measured by a galvanometer. The engraved index line of the collective lens, located between the lamp and the galvanometer, is imaged upon the transmission scale of the colorimeter by the galvanometer mirror. Reflected light from the galvanometer mirror, the position of which is determined by the output current of the photocell, enables reading of percent transmission throughout the mineral sample being tested. The colorimeter, Fig. 1, was standardized as follows: 1-The colorimeter was connected to a Sola constant voltage transformer, A, of 6-v output operated from a 110-v ac supply. 2-Turning the toggle switch, C, illuminated the transmission scale, B, and the control knob, D, was adjusted with a blank in the optical system until the hairline on the scale read zero. 3-A No. 430 interference filter, E, was inserted into the filter channel, F. &--A test tube, G, containing 7 cc of distilled water was pressed into the sample space, H, and the fine adjustment knob,

Jan 9, 1954

By W. H. Moore, E. T. Powell

IN the early days of mining in the Anthracite field, only the thicker and better seams of coal were mined, because of the limited mining and coal-cleaning facilities, therefore many of the thinner and less productive seams were permitted to remain unmined. With improvements in mining methods, the introduction of modem preparation plants, and the increased market demand for small-size coal, the thinner and more laminated seams have now become assets. In many instances these seams overlie the mined-out beds of the thicker and better seams, from which all recoverable coal was removed by the conventional breast-and-pillar method of mining. Some collieries in certain sections of the Anthracite field are now relying on these thinner and laminated seams. For the purpose of illustration, a large area in the Hickory Swamp-Ridge Basin of the western middle coal field has been selected, where as early as 1898 the No. 4, or Little Buck Mountain, seam was mined and pillars removed. The No. 5, or Buck Mountain, seam lying on a comparatively light pitch and with intervening strata of but 55 ft. of rock was not mined until 1935. Farther east, in the same basin the Nos. 8 and 9 seams, which are two splits of the Mammoth seam, have been mined and robbed and the workings have been abandoned since 1896. The overlying No. 9 ¾ seam, or the upper split of the Mammoth, and the No. 9 ¾ or 4-ft. seam remained virgin, with only an interval of 50 ft. of rock separating them, and with 40 to 50 ft. of rock strata separating the No. 9 ½ seam from the completely mined area of the Nos. 8 and 9 seams. These seams lie on a pitch of 45° on the south side of the basin and on 75° on the north side of the basin. Mining has been carried on in the 9 ½ and 9 ¾ seams for 3 years on both dips of the basin, for a distance of 3500 ft. In some sections the overlying strata of the thicker seams previously mined have settled without any apparent breaks in the upper strata, as indications have shown in the top split of the Mammoth; while in other areas the roof and bottom of this top split of the Mammoth have settled unevenly, thereby causing the bottom and roof to break into blocks. In attempting to mine over a large area of the No. 5 or Buck Mountain seam, a similar settlement has been encountered; the roof of the seam has been broken and a considerable amount of timbering has been necessary in order to make the mining of the seam possible. The conventional breast-and-pillar method, using shaker conveyors, has been used in the No. 5 seam, and a slant-breast method in the mining of Nos. 9 ½ and 9 ¾ seams. MINING OF LIGHT-PITCH SEAMS The No. 4 seam was mined and robbed by the conventional breast-and-pillar system. In this area the seam pitched from 5° to 25° on the north dip, averaged 8 ft. in thickness and had a slate bottom and a

Jan 1, 1941

By Philip W. Moen

It is with sincere regret that the members of the Institute will have heard of the death, on March 17th last, at Terre Haute, Ind., of Professor Charles 0. Thompson, A.M., Ph.D., President of the Rose Polytechnic Institute of that city, and for many years pre viously the head of the Worcester County (Mass.) Free Institute of Industrial Science, and in 1881 and 1882 one of the managers of this society. To us he was chiefly known by the excellent character of the work which he had performed, as a recognized leader among the technical educators of the country. He was a constant, and interested atten dant at our meetings, seeking to acquaint himself not less with all that was noteworthy in the practical attainments and developments of the branches of industry represented by our membership, than with such such facts as would be of service to him in shaping or guiding a wise course of instruction in the institutions of which he had charge. We shall not soon forget him, or the genial courtesy of his manner, or his ready words and thoughtful comments. Charles Oliver Thompson was born September 25th, 1836, at East Windsor Hill, Conn., where his father, Rev. William Thomp son, D.D., was professor in the Connecticut Theological Seminary, since removed to Hartford. The son was fitted for college under the late Paul A. Chadbourne, and entered Dartmouth College in 1854. He was graduated in 1858 with honors. In all the studies of his course he had maintained a high rank, but showed marked proficiency in chemistry and mechanical philosophy. In 1861 he received the degree of A.M., followed by that of Ph.D. from his own college in 1879, and from Williams in 1880. In September, 1858, the year of his graduation, he became principal of the Peacham Academy, Vt., remaining in that position until November of 1864, though during that period he devoted several months to practical work as a surveyor and civil engineer. Thus his experiences were developing the qualities which, later on, fitted him to carry out so successfully the plans of the thoughtful projectors of a new system of technical education, along a path before untrodden, but which the test of time and the indisputable proof of success have shown to be both wise and fruitful.

Jan 1, 1886

Inflation, fuel shortages, environmental restrictions, and a worldwide recession that sharply curtailed the demand for goods and services, were the main causes for the poor performance & virtually all industrial minerals in 1975. This poor showing was not a surprise. As Felix Shay correctly predicted in his introductory remarks to last year's industrial Minerals Review (ME, Feb. 1975, p. 70), ". . . the minerals industry will soon be facing falling demand as a consequence of sharp declines in auto production, housing, appliances, and other consumer goods. Moreover, when sales weaken. the high-volume, low-priced industrial minerals will incur sharply.

Jan 3, 1976

By J. Howard Boyce

INTRODUCTION The Tsumeb Mine is situated in the northern part of South West Africa, approximately 335 air miles north-east of the port of Walvis Bay on the Atlantic Coast, and 240 air miles north of Windhoek, the capital of South west Africa. The mine came into operation in the early 1900's and has operated continuously since then except during the two world warm and the depression years of the thirties, Tsumeb Corporation purchased the property in 1947, installed a new plat, and ham built a modern tom. In addition to the concentrator which began operations in 1948, a copper smelter was started in 1962 and a lead smelter in 1963, Tonnage of ore treated in the concentrator has varied through the years, reaching a maximum of 70,000 tons per month with a current mined tonnage of approximately 50,000 tons per month. Copper concentrates, lead concentrates and zinc concentrates are produced, and for a number of years the production of a germanium enriched concentrate was an important feature of the operation, Both copper and lead concentrates are smelted in Tsumeb, while the zinc concentrates are shipped overseas. Ore change, and the installation of the smelters in Tsumeb have necessitated modifications in the concentrator operation. This paper will describe current plant practice in some detail and will touch briefly on the techniques used from 1954 to

Jan 1, 1970

By Ronald C. Koo

SMALL additions of potassium, aluminum, and silicon as oxides (referred to as dope) to tungsten have been known for several decades to have a very large effect in raising the recrystallization temperature and altering the recrystallized grain morphology of heavily drawn wire. Previous investigations of this doping effect1 6 have led to various speculations but all failed to deduce unequivocally the physical state or the mechanistic influence of the dopant. Recently, walter7 has observed, by transmission electron microscopy, strings of "fine particles" in heavily rolled and annealed doped tungsten sheet and concluded that they were particles of mullite (Al6Si2013). His conclusion was inferred from the electron diffraction patterns of large particles ex-trated by carbon replication of fractured surfaces of slabs rolled from sintered ingots. That the strings of "fine particles" in heavily rolled and annealed sheet were also mullite was an assumption for which no evidence was presented. A similar investigation has been carried out in this laboratory over the past 2 years on a variety of tungsten wire: doped tungsten, and undoped tungsten, as well as 218 doped tungsten purchased from the Lamp Metals and Components Department of the G.E. Lamp Division. Although the electron microscope observations are similar to those reported by Walter, the writer has reached a different conclusion concerning the physical state of the dopant in annealed tungsten. The purpose of this communication is to present evidence that the strings of "fine particles" observed in transmission specimens are not mullite, but are voids. In the present investigation, tungsten wire, 0.88 mm in diam, was rolled into ribbon 0.2 mm by 125 µ thick. The ribbons were annealed in vacuo at a pressure of -1 x 10-5 Torr and then thinned electrolytically in a 2 pct KOH solution. Fig. 1 shows a typical transmissicjn electron micrograph of a sample annealed at 1700°C for 30 min which reveals rows of closely spaced voids having a light contrast (referred to as "fine particles" by Walter) aligned parallel to the working direction. Stereo micrographs (by D. Moon, Westinghouse Research and Development Center) have shown that these voids do not exist on the surfaces of the specimens as a result of thinning but are within the thin-foil specimens. The following experiments have been performed to verify that these are indeed voids. I) Effect of Annealing. Voids are absent in unannealed specimens and appear only after annealing. This behavior cannot be explained if they were solid particles such as mullite. Precipitation (in an unquenched specimen) upon annealing requires solute elements having decreasing solubilities with increasing temperature. Although the solubility of aluminum in tungsten does decrease with increasing temperature, precipitation requires a concentration in excess of 1.4 wt pct,8 which is at least two orders of magnitude higher than the aluminum content in doped tungsten. It is also unreasonable to assume that particles aligned in rows initially present in unannealed specimens were too

Jan 1, 1968

Jan 1, 1969

United Engineering Trustees, Inc. ARTHUR S. DWIGHT GEORGE D BARRON J V. N DORR Engineering Societies Library Board ROBERT PEELE PHILIP W. HENRY GEORGE C STONE JOSEPH E. POGUE The Engineering Foundation H C BELLINGER GALEN H CLEVENGER J V N DORR

Jan 1, 1923

By William B. Plank

ENROLMENT data given in this report of the seventh study of the schools by the Mineral Industry Education Division reveals the critical situation in the mineral engineering schools of the United States. Complete figures for the year 1942-43 show that at that time, about one year after Pearl Harbor, the enrollment of mineral engineers was 6385 or 30 per cent less than in 199441. By October 1943, however, enrollment had dropped to 2050, as reported in the Journal of Engineering Education of January 1944. This was a further reduction of 68 per cent in one year, or 77 per cent in three years. With accelerated programs in effect during the current year, with many graduations since last October, and with the military forces taking practically all the high school graduates, the present enrollment is, of course, much lower than the 2050 above given. There are no late data on the exact situation. In Canada, the same situation exists in the mineral engineering schools, only

Jan 1, 1944

By H. M. Fisher, R. E. Snow, S. C. Sun

RAPID colorimetric estimation of the amount of transparent minerals has been applied successfully to instream mill products at the cryolite flotation plant of the Pennsylvania Salt Mfg. Co., Na-trona, Pa. Apparatus used was a Bausch & Lomb monochromatic colorimeter. The optical assembly of the colorimeter, shown in Fig. 1, passes light from a 6-v, 32-cp, prefocus incandescent lamp through two condensing lenses, a heat-absorbing filter, an aperture-control diaphragm, an interference filter, and a sample container. The light finally strikes a barrier-layer photocell and the output current of the photocell is measured by a galvanometer. The engraved index line of the collective lens, located between the lamp and the galvanometer, is imaged upon the transmission scale of the colorimeter by the galvanometer mirror. Reflected light from the galvanometer mirror, the position of which is determined by the output current of the photocell, enables reading of percent transmission throughout the mineral sample being tested. The colorimeter, Fig. 1, was standardized as follows: 1—The colorimeter was' connected to a Sola constant voltage transformer, A, of 6-v output operated from a 110-v ac supply. 2—Turning the toggle switch, C, illuminated the transmission scale, B, and the control knob, D, was adjusted with a blank in the optical system until the hairline on the scale read zero. 3—A No. 430 interference filter, E, was inserted into the filter channel, F. 4—A test tube, G, containing 7 cc of distilled water was pressed into the sample space, H, and the fine adjustment knob,

Jan 1, 1955

By W. E. Bron, E. S. Machlin

GRAIN boundary migration in V-shaped thin specimens of high purity silver was studied. Each specimen contained two crystals having the relative orientation: (111)A/(111)B; (ll0)A/(101)B. The boundary between these two crystals varied between a continuous curved and an alternating two plane interface. The plane interfaces were oriented parallel to (101)A/(011B) and (121)A/(211)B. Traces of these planes are shown in Fig. 1. Evidently the two plane interface, although of higher area, comprises lower total interface energy than the average curved boundary it replaced. The plane boundaries were found to move at 650 °C to consume the broad segment of the V opposite to the direction of interface area and energy decrease. On investigation, using the thermal etching technique of Hendrickson and Machlin,1 it was found that the outer grain contained 8.3x108 more dislocations per cm" than the grain at the apex of the V. Consequently, the boundary moved to decrease the strain energy associated with the difference in dislocation density across the boundary. The rates of motion of specific {110} and {112} boundaries were measured during interrupted anneals at 650°C by referring the position of the boundaries to each other and a fiducial line on the specimen surface. The measured rates of motion are 0.075 and 0.025 mm per hr for the {110} and {112} boundaries, respectively. Plots of grain boundary motion vs time of annealing show straight lines with little deviation of data points from these lines.

Jan 1, 1957

By Benjamin Smith Lyman

The question of the original extent of the anthracite-beds of Pennsylvania has often been raised; and even discussed with reference to the probability of their present existence under the New Red, a matter of immense practical importance. So high an authority as my revered master, J. P. Lesley, Honorary

Jan 1, 1903

By F. M. Lewis, J. E. Goodman

A larger, slow-speed, under-loaded ball mill and hydraulic classifier have almost doubled grinding efficiency at the lsabella mill. TENNESSEE Copper Co. operates two ore con-A centrators, the London and Isabella mills near Copperhill, Tenn. In 1948 and 1949 the small ball mills and rake classifiers in the London concentrator were replaced by one large ball mill and one hydraulic classifier. This new ball mill was designed oversize so that it could be operated at slower than normal speed. The proper operating conditions were established and the results published.' Later it was found that this mill operated more efficiently with a small ball charge." While this London grinding practice was being developed, the Isabella grinding circuit was not changed in any way. It remained a conventional two-stage rod mill—ball mill combination, the rod mill in open circuit and the ball mill in closed circuit with a rake classifier. Study of the data indicated that grinding cost could be lowered by converting to the London practice, but not enough would have been saved to warrant the expense of converting. No plan for improving this grinding operation could be developed. In 1953 this study was reopened when plans were made to increase the Isabella mill output from 1150 to 1500 tpd. At this time the grinding circuit consisted of a 6x12 rod mill followed by a 6x12 ball mill in closed circuit with a 6-ft rake classifier. Another 6x12 ball mill and 6-ft rake classifier would have been sufficient equipment and would have been the simplest and cheapest installation. However, this would have offered no improvement in grinding efficiency or operating cost. If, on the other hand, the grinding operation could be converted to the London practice, by installation of one large 101/2x9x9 tricone mill and a 10-ft hydroscillator,2 lower operating costs would justify the additional investment. Economics: Table I presents estimates for the two schemes for enlarging the Isabella mill. In the first scheme, column 1, one 6x12 ball mill and one 6-ft rake classifier were to be added. In the second scheme, column 2, the existing small ball mill and rake classifier were to be retired and one large mill and hydroscillator were to be installed. Estimated savings from the difference in operating costs made an attractive return on the additional investment for the large mill and hydroscillator. Actual costs of carrying out this plan are tabulated in column 3b. It will be seen that these costs follow the estimates in column 3a very Closely. The return on the additional investment is calculated from the difference in the operating cost in column 1 and the actual operating cost in column 3b. This too come very close to the estimate. Power and Steel: Power requirements and steel consumption for the rod mills and ball mills, both actual and estimated, are presented in Table 11.

Jan 1, 1958

By Caner Zanbak, Erdogan Yüzer, Mahir Vardar, Kemal A. Erguvanli

The Hasancelebi iron deposit in Eastern Turkey is a very low grade (average 20% oxide) magnetite body consisting of 720 million longtons of proven reserve at a 10% cut-off limit. The ore-bearing scapolitic oclcs cover an area of approximately 4300m x 300m, and the thickness of the outcropping deposit exceeds 300m. Prefeasibility project studies revealed that a one degree decrease in a 45° final slope angle of the proposed pit would require excavation of approximately 10 million cubic meters of excess waste material, for a projected pit bottom 300 meters below the valley floor. There- fore, determination of the final slope angles of the open pit was considered to be the most important task in the feasibility analysis of this project. In this investigation, the main emphasis was given to collection, compilation and evaluation of the engineering geological, hydrogeological and rock mechanics data of the highly fractured and weathered rocks. Due to the presence of intense fracturing, the rock wedge analysis method was used for projected 30m-high benches and the circular failure analysis method was used for the stability of the projected final pit slopes. The proposed bench slope angles ranged between 60° and 80°, whereas the projected final slope angles varied between 30° and 48°, depending on the slope heights and groundwater levels.

Jan 1, 1983

By O. C. Ralston

The use of copper sulfate for improving the flotation behavior of sphalerite is probably at least 15 years old. The original discovery of its activating influence is somewhat obscure. The story goes that in the mill at Mascot, Tenn., its favorable action was discovered by accident, early in 1914, as follows: The original laboratory test work on a sphalerite ore gave favorable flotation results, but after a mill had been built the flotation concentration of the ore was very unsatisfactory. In diagnosing the probable reasons, one fact pointed out was that the laboratory test machine had been constructed of bronze whereas the commercial machine allowed pulp to come in contact only with wood and iron. A plate of sheet copper was hung in the flotation machine and results immediately improved. At first fanciful explanations of electrolytic and electrostatic behavior were given credence, but when the copper plate was removed and a small amount of copper sulfate substituted in the pulp an even more favorable result was obtained. Toward the end of 1914 copper sulfate was also adopted in the acid flotation circuit of the Butte and Superior Copper Co. Just who is responsible for the original discovery the present writers do not know. It seems strange that in that era of flotation litigation this discovery was not patented. While for pragmatic purposes it [nay be sufficient to know that the mere addition of copper compounds to a flotation pulp is sufficient to activate the flotation of the sphalerite, for scientific purposes it is quite desirable to know more about how the action takes place. It is the purpose of this paper to present certain evidence dealing with the mechanism of the beneficial effect. The description of the effect as activation in contradistinction to depression is now common in both the English and German languages. It makes no assumptions as to whether the zinc sulfide surfaces have been filmed with copper compounds. In fact, the principal differences of opinion expressed in the literature deal with whether there is an actual formation of CuS (or even Cu2S) on the surface of the sphalerite. Activation of sphalerite takes place in alkaline, neutral or weakly acid solutions and whereas the present day flotation of sphalerite is usually in ah alkaline solution, the early use of copper sulfate was in a sulfate solution.

Jan 1, 1930