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By E. A. Moulder

The mining industry is continually faced with problems involving dewatering, pollution, water supply, leaching and hydrochemical mining and prospecting. Greater application of the principles of ground-water hydrology to solution of these problems promises improved operating efficiency, increased safety and better public relations. Estimating the magnitude of dewatering for a proposed mine may be a major factor in determining the feasibility of proceeding with mine development. Diverting the source of ground water to an abandoned mine may save costly treatment of acid-mine drainage. Development of a large ground-water supply near an ore deposit may enhance the possibilities of a leaching operation. Detection of certain dissolved minerals in water from springs or wells may lead to hitherto unknown mineral deposits. Current efforts of industry, educational institutions and government are making these kind of events more commonplace. Dewatering of Mines The magnitude of dewatering problems was dramatized by a flooding that occurred last year in a gold mine in South Africa. During drilling operations at the West Driefortein mine, a major fracture was encountered from which large volumes of water issued necessitating evacuation of 1350 men from the mine. Dewatering required an increase in pumping of more than 80 million gpd. Models of ground-water systems are being used to test alternate plans for dewatering mines. Using the models in conjunction with computer optimization programs may lead to minimizing costs of operation. In addition to computer simulation of aquifers associated with phosphate deposits in North Carolina mentioned in last year's report, two USGS employees developed a model to estimate the amount of pumping required to dewater a mine site in Colorado.

Jan 1, 1970

By A. J. Turk, R. G. Dalbke

An increasing number of water pollution control systems are certain to be installed by many industries in the future because of new federal, state and local government regulations, and because of the rising general concern about the deterioration of our water resources. Extensive engineering, some of it based on methods not yet developed, will be required if these new systems are to provide optimum pollution control. Among the primary design factors to be considered are capital cost, operating cost, and present and future regulatory requirements. Establishing A Survey and Test Program To produce a final plant effluent meeting regulatory agency requirements, engineers must have background data that are accurate and representative of present and future plant operation. Operating and plant engineering departments often have available much information, including plant water quantitative and qualitative requirements, both present and future, that can be helpful in the preparation of designs of pollution control systems.

Jan 5, 1968

By D. E. Pickett, E. G. Joe

In accordance with good industrial practice, Canadian metallic-ore concentration plants have always recycled a high proportion of process water to save reagents, save power, conserve water resources, and to protect the community water supplies, to give only a few reasons. In the last few years there has been awakened public concern for the environment and, consequently, government regulations have been added as additional reasons. Present recycling practices are summarized as a basis for improved plant design and operating procedures and for further research. In addition, an attempt is made to determine why plants do not recycle water in certain situations. Although not all Canadian mills are covered, the many examples given indicate the problems and the effort being made to solve them. Wherever available, the chemical quality of the water and the process requirements are indicated as well as the other parameters affecting water recycling at each operation.

Jan 1, 1975

By Marcel Daly

(A contribution to the study of the conditions of equilibrium of the "free surface" of a water body inclosed in a porous medium.) IN a recent paper, on Geologic Structure in the Cushing Oil and Gas Field, Oklahoma,1 Carl H. Beal has pointed out some interesting peculiarities in the distribution of the hydrocarbons and the disposition of the "planes of separation" between the oil and the water (water surfaces). Mr. Beal's principal statements on this matter may be summarized as follows: I. In every important dome in the Cushing field, which has not been complicated by folding along its sides, the oil area in each, of the three oil and gas sands studied (Layton, Wheeler and Bartlesville) apparently extends farther down on the long axis. of the dome than it does on the steeper sides. The result is that water is encountered at a lesser depth below datum plane (sea level) on the steep sides of the dome than along the ends where the beds are more gently tilted. II. In the Layton and Wheeler sands (to which the detailed study of water surfaces has been almost entirely confined), the water surface is not level, but dips at a gentle angle (maximum dip 100 ft. to the mile) away from the center of the structure. This inclination existed prior to development, and it has been rendered greater by the rapid extraction .of oil and gas. To these statements, the following observations are added. The dominant structural feature in the Cushing field is a broad north and south anticlinal fold, along whose, axis the domes are distributed (Fig. 1, p. 1104), and the more important oil areas in each sand lie on the west side of the field. In many cases, gas has been forced to the east side of the structure, sometimes as far as the water line. From the distribution of the oil and gas bodies, Mr. Beal concludes that the hydrocarbons in this region probably migrated from the west or the northwest.

Jan 1, 1918

By Dorsey Hager

THE rapid increase of water troubles in the Mid-Continent oil fields is causing much alarm. Troubles occur at Towanda, Eldorado, Augusta, Cushing, Blackwell, and Healdton, although they had, not been acute in the Mid-Continent field until about two years ago, when the unusual conditions in the deeper oil fields were first encountered. California faced the same situation, but, thanks to aggressive measures, has largely overcome the dangers. The following analysis of water trouble may throw some light on the subject and be of assistance in solving the problems involved. WATER TROUBLES CLASSIFIED The presence of water in large quantities in oil sands has the following results: 1. Diminishes oil production. 2. Diminishes casing-head gasoline production: (a) By curtailing the gas flow. (b) By making the use of vacuum pumps unsuccessful. 3. Increases lifting costs: (a) By making it necessary to pump large quantities of water, which requires. a fast motion and long stroke (third hole). (b) By requiring the use of compressors for air lift. (c) By causing break-downs and delays due to the high speed necessary to pump water. (d) By making it necessary to treat "cut" or emulsified oil. Oil production is seriously curtailed by the presence of large quantities of water. Lease records show that wells are shut down 40 to 60 per cent. of the pumping time where serious water trouble occurs. While a small quantity of salt water may cut the paraffine and keep the oil moving, several hundred feet, or a hole full of water, effectually "kills" the oil

Jan 10, 1918

I. N. KNAPP, Ardmore, Pa. (written discussion *).-The writer would first call attention to the fact that the mid-Continent field was credited from 1900 to 1915 with a production of about 641,000,000 bbl. of oil with-out any burdensome water troubles being reported. In fact, the authors say the conditions were not acute until about two years ago when the unusual conditions in the deeper oil fields were first encountered. The writer disclaims any personal knowledge of the district mentioned but, from the experience he has gained in directing drilling in various fields by both the cable-tool and the rotary methods and also in plugging and cementing wells, he fails to see how the analysis of water trouble given in the paper under discussion could be of any practical assistance in solving the problems so vaguely outlined. Possibly it might induce academic discussion, if not limited to practical operating conditions. A recent bulletin of the Bureau of Mines gives definite and practical statements that can be easily understood by one skilled in the art of drilling wells and heading off water troubles. From an operating standpoint subsurface knowledge must be based on logs of completed wells. Absolutely no one can have such knowledge as that indicated in Fig. 1 of the paper in question without drilling wells, and no one can question such facts when disclosed by the drill. Under classification of water the paper states "This water (primary) cannot be exhausted from the sands, but its encroachment can often be checked and so directed that wells need not be abandoned, until most of the available oil is secured." This is a live question to the writer. A couple of years ago he had some wells drilled and found the conditions comparable with sands A and D of Fig. 1 with B and C left out; but nothing in the paper, so far as can be found, indicates how this water encroachment is or can be checked or directed particularly under the High heads named.

Jan 5, 1919

By S. J. Hubbard, S. D. Michaelson, A. W. Last, B. H. Ensign

Of the seventeen western states, five-Arizona, Utah, New Mexico, Montana, and Nevada-produce about 90 pct of this country's primary copper. All seventeen of these states occupy 60 pct of the nation's land area but receive only 25 pct of the country's total precipitation. Seventy percent of this precipitation returns directly to the atmosphere through evaporation and transpiration, leaving very little for ground reservoir recharge or immediate domestic, agricultural, or industrial use. With so limited a supply available for all, competition for water rights among users is severe. The result does not always permit using the limited supply to produce the most valuable end product. Most of industry and much of agriculture can shop around for suitable operating locations. Where water is critical to their purposes, they can and do locate in areas where the needed amounts are available. Such is not the ordinary lot of the mining industry, which must locate in the area of the deposit it is planning to mine and concentrate. In the case of copper this happens to be, for the most part, right in the heart of the semi-arid regions of the West.

Jan 7, 1960

By S. H. Ash

IN no part of the world other than a small area in Pennsylvania is anthracite mining an industry of major magnitude. As the deposits of anthracite in the United States are limited virtually to Pennsylvania, the difficulties of this industry have been commonly considered a state rather than a national problem. However, there is also national interest in the conservation and wise utilization of all the country's fuel resources and in the control of interstate waterways. The anthracite industry is confronted with a serious problem of water accumulation in many of the mines, a problem that must be solved in the near future if progressively higher mining costs are to be avoided. It cannot be solved by the operating companies without state or Federal aid, or both, owing to the magnitude of the work required, the diversity of interests of the coal and surface ownerships, the hazard to the whole mining community, and interests affected outside the mining region. 'The costs of abating the ever-increasing surface seepage to mine workings and of handling this seepage once it has occurred are beyond the eco¬nomic resources of the operating managements.

Jan 1, 1941

By Wm. C. Coffin

THE refractory linings of open-hearth steel furnaces above the bath line are subject to severe wear not only from the heat caused by the combustion of the fuel and the reactions of the bath, but also from the melting action of the gases when not controlled and directed, and from the scouring of the oxides, etc. with which the products of combustion are charged. The framework that encases or binds the furnace is made up primarily of an iron or steel pan in which the furnace proper is built, side and end buckstays, and tie-rods. The expansion and contraction are so great and variable that the bindings may be subjected to severe stresses unless the tie-rods are carefully adjusted in heating up the furnace, but they are most affected by direct heat and usually become deformed from that cause when the lining is worn thin and, sometimes, when sections of the lining fall in and expose some of the framework. A deformed framework displaces the skewback of the roof arch and tends to distort or crush the roof. Bent buckstays deform the front wall, causing the door frames to stand away from the lining so that the gases burn between the lining and the frames, destroying both of them. Frequently the frames are attached to the buckstays; then when the latter bend the frames usually break. Preventing the distortion of the framework and maintaining the economy of the refractories are real factors in the cost of steel making. Not only does the cost of general repairs and reconstruction add directly to the cost of steel produced, but the time lost in making repairs cuts clown the steel production and increases the overhead expense of both the furnace shop and its allied foundry or mills. Many years ago water-cooled equipment applied to iron blast furnaces made it possible to increase greatly not only the size and production of the furnaces but also the life of the lining. It also cut down the loss from frequent repairs. The open-hearth furnace is a much later invention, especially as a commercial factor; for though it dates from the Fred Siemens patent of 1856, much more progress was made in the Bes-

Jan 2, 1919

J. S. UNGER,* Pittsburg, Pa, . (written discussion?).-The author of the paper has given an excellent description of the appliances used to cool parts of an open-hearth furnace, and some of the reasons why the refractories fail in service. Personally, I favor water-cooling, but to a limited degree. At one time I advocated more universal cooling than is now practised, but believe I must change my mind. Water-cooled, thin-lined blast furnaces have not proved as satisfactory as anticipated. While this may retard the building of many such furnaces, it will not prevent the use of regular tuyere- and bosh-cooling appliances. Water-cooling any furnace may be easily carried to the extreme. In an open-hearth furnace, excessive port or roof cooling, or cooling the working floors may preserve the lines of the furnace, lower the cost of refractories, acid to the comfort of the workmen, and necessitate fewer shutdowns for repairs, but it may not be good economy on account of the high first cost, the cost of cooling water, maintenance of cooling appliances, and the immediate reflection in a higher fuel cost. The question becomes a financial one, and is answered by using water-cooling devices up to the point at which they cease to show true economies. Open-hearth furnace bulkheads, roofs, and ports fail rapidly in about the order named. If they could be made to last indefinitely by water-cooling, the furnace would still have to be shut clown periodically for cleaning the slag pockets, regenerator chambers, and flues. Extra, or spare, pockets and regenerator chambers have been advocated to permit of continuous operation, but the space required, the cost of installation, and the fuel required to initially heat such cold chambers will largely prevent their adoption. Some particular fuels, as high-ash powdered coal, require frequent stoppages for cleaning, but for this particular fuel a special provision can' be made.

Jan 5, 1919

ROBERT M. KEENEY,* Portsmouth, Ohio (written discussion?).- Mr. Coffin has written a most interesting paper that covers most of the uses to which water-cooled devices are subjected; but to meet with the operating department's approval, these devices must effect a saving in cost per ton of ingots produced in the furnace. The making of steel in the open-hearth furnace is dependent entirely on the personal element. It is not possible to charge the furnace with so much raw material, turn on a valve for heat, and by use of recording thermometers, clocks, etc. empty the furnace when a steel is made. Competent men trained to the work must be in charge all the time, and the quality and quantity of steel produced is quite as dependent on the care and working qualities of the furnaces as on the raw material and working of the charge itself. Steel making is hot, hard work and the inducement offered to technical men to take up this work is not sufficient to induce many to enter the field. The result is that most of the workmen in an open-hearth plant, the men who actually operate the furnace and make the steel, are not technical men and do not understand the "whys" and "wherefores " and care less. All this means that a furnace must be built as nearly fool-proof as possible. By this I mean that it is necessary to protect those parts of a furnace most subject to abuse by water-cooled devices whenever possible, and these water-cooled appliances must he as nearly fool-proof as they can be made. The control of the gas entering a furnace is of the utmost importance. This means a properly designed port must have the same design throughout the whole run of the furnace. This is not possible with the ordinary

Jan 6, 1919

By Suresh P. Babu, Joseph W. Leonard

The ultimate objectives of comminution should be to reduce material to some specified size while producing a minimum of undersize or fines, with less power, higher throughputs, and with more compact machinery. Attempts to achieve these objectives have been only partially successful, since gains in some areas are achieved at the cost of concessions in other areas. An example of some of these trade-offs can be found in the closed circuit crushing operations of the anthracite and crushed stone industry where, in order to produce a minimum of unprofitable fines, unfavorable concessions must be made in the size of the crushing facility where 2 or more crushing stages are interphased by 2 or more screening operations. This paper discusses experiments with a new process which attempts to achieve some, if not all, of the comminution objectives in a single pass operation without undesirable concessions; or, at the very least, to achieve more than is possible with systems in use today. These objectives are sought by use of water-flushing to enhance comminution. The crushing of coal and other minerals is a mature technology that is long overdue for a careful re-examination. Crushing of coal is generally achieved through the use of rotary breakers and roll crushers. Water-flushing, as envisioned here, appears to have potential application in the following areas: 1) For primary raw coal crushing or for secondary crushing of rotary breaker products. 2) For use as a size reduction and/or concentrating step for crushing coal mine refuse from present production or from existing refuse dumps. 3) For possible future application in underground preparation interphased with continuous mining machinery. Size reduction with conventional methods is known to be an inefficient operation when the increase in surface energy of the material crushed is compared with the input energy. A simple breakdown of the energy consumption in size reduction, given by Orr, is shown in [Fig. 1]. It is believed that most of the energy supplied is lost in the form of interparticle friction.2 Hence, the removal of fines immediately after their formation or the implementation of steps to prevent their formation, based on reduced friction, will reduce the energy requirements of the communition operation.3 A detailed discussion of the mechanism of size reduction is available in other literature.3-5 Even though the closed circuit crushing operation is designed to carry the fines away from the crushing zone, it is still inadequate for instantaneous removal of fines. The present investigation advocates the use of a flowing liquid medium to remove the crushed product immediately after size reduction. Unlike the wet-grinding methods, no constraints are required for the liquid flow rate, and, also, the liquid medium can be used in primary crushers like jaw crushers, hammer mills,

Jan 1, 1978

By JULIAN HINDS

Industrialization is raising the standard of living of people everywhere. The common man is demanding and getting more of everything. Perhaps more markedly than most other things, he is consuming more water. A hundred years ago water for domestic use, in all but a few large centers, was lugged from wells in buckets. This still is true in many rural areas, even in the enlightened United States of America. but pumps and pressure systems are rapidly replacing the "old oaken bucket," even on farms and in isolated country homes. Nevertheless, many still fail to see water as a ?commodity? in the same sense that coal, lumber, fertilizer, and bread are considered as commosities. Water is too frequently taken for granted.

Jan 1, 1949

IT has been discovered by skilled bell founders, more through experience than from geometrical calculation (although calculation does enter), that a certain relationship of dimensions in both large and small bells makes the tone and the weight almost certainly what is desired. This is in addition to the customary shape which is, according to the historians, perhaps that found by the first discoverers of bells. Among themselves bell founders have made a rule of these measurements and have called it the bell scale. Beginning with the small ones weighing ten pounds, it increases by degrees to a point where, as I have seen, they are able to make them even twenty-five and thirty thousand pounds. This scale is of great enlightenment if one does not have a bell already made for comparison.

Jan 1, 1942

By Fred Bond

THE process of comminution by grinding is properly classified as an art, rather than as a science. Like most other operations concerned in ore dressing, or in the treat-ment of nonmetallic minerals, the mathe-matical relationships of rock breaking are still obscure, and much disputed. If some basic formula exists, comparable for in-stance to E = RI in electricity, it has not yet been placed in common use. The absence of such a comprehensive mathe-matical background undoubtedly is the cause of many inefficient designs and installations, as well as of much poorly oriented experimental work. On the other hand, the mathematical immaturity of the process constitutes an opportunity for a real contribution on the part of those who enjoy mental pioneering. Some of the statements made in any such exploratory work may be little more than opinions, and it is to be expected that some will later be proved untrue; but such an evolutionary development is necessary if we are ever to arrive at the fundamental laws, the discovery of which can change the empirical art into a mathematically exact science. The most significant principle of com-minution that we possess is probably Rittinger's law, which states that the work done in crushing or grinding is proportional to the area of the new surface produced. There is an alternative theory, known as Kick's law, which formerly was preferred to Rittinger's but which now is rather dis-credited. According to Kick, the work done in comminution is proportional to the volume, or weight, of the pieces broken, or to the cube of their diameters, while accord-ing to Rittinger it is proportional to the square of the diameters.

Jan 1, 1940

By Fred C. Bond

THE process of comminution by grinding is properly classified as an art, rather than as a science. Like most other operations concerned in ore dressing, or in the treatment of nonmetallic minerals, the mathematical relationships of rock breaking are still obscure, and much disputed. If some basic formula exists, comparable for instance to E = RI in electricity, it has not yet been placed in, common use. The absence of such a comprehensive mathematical background undoubtedly is the cause of many inefficient designs and installations, as well as of much poorly oriented experimental work. On the other hand, the mathematical immaturity of the process constitutes an opportunity for a real contribution on the part of those who enjoy mental pioneering. Some of the statements made in any such exploratory work may be little more than opinions, and it is to be expected that some will later be proved untrue; but such an evolutionary development is necessary if we are ever to arrive at the fundamental laws, the discovery of which can change the empirical art into a mathematically exact science. The most significant principle of comminution that we possess is probably Rittinger's law, which states that the work done in crushing or grinding is proportional to the area of the new surface produced. There is an alternative theory, known as Kick's law, which formerly was preferred to Rittinger's but which now is rather discredited. According to Kick, the work done in comminution is proportional to the volume, or weight, of the pieces broken, or to the cube of their diameters, while according to Rittinger it is proportional to the square of the diameters. Careful determinations of size distribution below the limit of sieve sizes1 indicate strongly that under ordinary grinding conditions the amount of new surface area produced is directly proportional to the net power input. Changes in the size ratio between the balls and the particles cause important differences in the proportion of the product that passes a given mesh size, but do not affect the total amount of new surface area; they merely change the distribution of the surface among mesh sizes. The principle of constant surface area is the logical result of Rittinger's law, and it may well have an important bearing on the comminution theories of the future. FORMULA FOR BALL WEAR Grinding tests have been made in the Allis-Chalmers laboratory for more than 9 years, using a standard charge of mixed balls of different sizes; and a continuous record has been kept of the rates of wear of each size. These results have been combined and plotted in various ways in order to discover the relationship that exists

Jan 1, 1940

By D. E. Norquist, J. E. Moeller

The results of wear on marked balls, 4, 31/2, 3, and 2 in. diam are given. All balls were forged steel of practically the same chemical analysis and hardness. The results indicate that balls in a given mill for a given length of time will have equal diameter losses, regardless of size.

Jan 1, 1950

By C. M. Loeb, T. E. Norman

THE use of ball, rod and tube mills for grinding ore, cement and other materials has grown so rapidly during the past forty years that the world's annual consumption of ferrous grinding media for these mills is now estimated to be between one half million and one million tons per year. Ferrous grinding balls constitute the major portion of this tonnage. Obviously they represent sufficient value to justify thorough studies' of the factor sgoverning their performance. The selection of grinding balls is governed principally by: I. Quality (wear resistance, impact resistance, soundness, and the like). 2. Sources of supply and delivered cost. 3. Grinding characteristics or efficiency in the ball mill. This paper deals principally with the quality of ferrous grinding balls. In the study of these factors certain data relative to the fundamental nature of ball wear in ball mills have been obtained. These data are also presented and discussed briefly. THE DEVELOPMENT OF A SUITABLE WEAR TEST A study of the fundamental factors governing the quality of grinding balls has been hampered seriously by the fact that a competent test has, in the past, involved the purchase of several hundred tons of balls of a specific type which were then run in one or more ball mills for a period ranging from several months to several years' duration. Often, during the period of test, it became necessary to change operating conditions or the character of the ore fed, to the test mill with the result that the rate of ball consumption changed and the test figures became of little value. Under such circumstances, progress in the development of better grinding balls, has been necessarily slow. Economic factors and variations in the quality of balls produced by different sources of supply generally make it necessary for each mill operator to determine for himself the most suitable type of balls for his mills. In our own ball mill grinding operations at Climax, Colo., we were faced with this problem. After we had run a few large scale wear tests at considerable expense we decided to investigate the possibilities of a small scale wear test which would be capable of testing numerous types of balls within a relatively short time. The most important requirement of any test is, of course, that it give results which can be used to predict accurately the wear in full scale operations. It was known that Ellis and his associates1,2 had developed a method of testing grinding balls by small scale tests run at the Ontario Research Foundation. Ellis' method of testing was used as a starting point in our investigations. In the course of our tests a number of modifications of the original method were found to be desirable so that, by an evolutionary procedure, a method of small scale

Jan 1, 1947

By C. M. Loeb, T. E. Norman

THE use of ball, rod and tube mills for grinding ore, cement and other materials has grown so rapidly during the past forty years that the world's annual consumption of ferrous grinding media for these mills is now estimated to be between one half million and one million tons per year. Ferrous grinding balls constitute the major portion of this tonnage. Obviously they represent sufficient value to justify thorough studies of the factor sgoverning their performance. The selection of grinding balls is governed principally by: I. Quality (wear resistance, impact resistance, soundness, and the like). 2. Sources of supply and delivered cost. 3. Grinding characteristics or efficiency in the ball mill. This paper deals principally with the quality of ferrous grinding balls. In the study of these factors certain data relative to the fundamental nature of ball wear in ball mills have been obtained. These data are also presented and discussed briefly. THE DEVELOPMENT OF A SUITABLE WEAR TEST A study of the fundamental factors governing the quality of grinding balls has been hampered seriously by the fact that a competent test has, in the past, involved the purchase of several hundred tons of balls of a specific type which were then run in one or more ball mills for a period ranging from several months to several years' duration. Often, during the period of test, it became necessary to change operating conditions or the character of the ore fed to the test mill with the result that the rate of ball consumption changed and the test figures became of little value. Under such circumstances, progress in the development of better grinding balls, has been necessarily slow. Economic factors and variations in the quality of balls produced by different sources of supply generally make it necessary for each mill operator to determine for himself the most suitable type of balls for his mills. In our own ball mill grinding operations at Climax, Colo., we were faced with this problem. After we had run a few large scale wear tests at considerable expense we decided to investigate the possibilities of a small scale wear test which would be capable of testing numerous types of balls within a relatively short time. The most important requirement of any test is, of course, that it give results which can be used to predict accurately the wear in full scale operations. It was. known that Ellis and his associates1.2 had developed a method of testing grinding balls by small scale tests run at the Ontario Research Foundation. Ellis' method of testing was used as a starting point in our investigations. In the course of our tests a number of modifications of the original method were found to be desirable so that, by an evolutionary procedure, a method of small scale

Jan 1, 1948

By C. E. Berry

NATURAL stone or manufactured porcelain pebbles are used as the grinding elements in pebble mills and the mills are lined with stone or porcelain blocks. Steel balls usually form the grinding medium in ball mills, and the mills may he lined with steel. Pebble mills are used to avoid contamination by metal of the material being ground, to avoid rapid wear due to corrosion, and for other specialized reasons. Belgian silex (silica) blocks formerly were used widely for lining pebble mills, because of their good resistance to wear, light color, and low cost, but the importation of these blocks was suspended early in the war. The stocks of Belgian silex diminished so rapidly that it was found desirable to compare the properties of a number of domestic substitutes for use in critical operations. Accordingly, a study was made to determine the best substitutes for fine grinding of white pigment and for certain heavy-chemical process work such as the disintegration of phosphate rock in weak phosphoric acid solution. A comprehensive survey of substitute lining materials was not contemplated. It was stipulated at the beginning of the investigation that only materials on the market, available in large quantities, would be tested and that these should be reasonable substitutes from a wear-resistance viewpoint as determined from known physical characteristics. Marble and limestone, for example, could be eliminated immediately. Quartzite, granite and porcelain were selected as likely substitutes for Belgian silex and were subjected to quality tests. MATERIALS TESTED I. Belgian Silex.-Sample blocks of a standard grade were taken from crates in which they had been imported. The stone was light gray in color and contained inclusions of small clusters of quartz crystals as well as light colored portions that might be calcite. This was a siliceous rock which appeared to be of igneous origin. 2. Quartzite.-Samples of quartzite were obtained from a quarry in Minnesota. The blocks exhibited a crystalline fracture. The stone was pink in color and composed of fine quartz crystals bound together with a siliceous cement. 3. Granite A was a fine-grained granite quarried in South Carolina. 4. Granite B was coarse-grained granite quarried in South Carolina. 5. Granite C was a coarse-grained granite quarried in North Carolina. 6. Porcelain A.-Sample blocks of the pebble-mill lining material were obtained direct from the manufacturer. It was white in color and of lower specific gravity than the natural materials. It did not have a crystalline structure. 7. Porcelain B.-Sample pebble-mill lining blocks of the porcelain were received direct from the manufacturer. It was white

Jan 1, 1946