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By William C. Buell

As used in connection with open-hearth or other high-temperature operations, "insulation" refers to a multitude of substances, natural or manufactured, that have the one principal property of preventing the flow of heat by conduction to a greater degree than refractories can prevent it, the principal properties of the latter being resistance to temperature and/or chemical action. The term "control" as commonly applied to the mechanization of management functions is inappropriate without qualification, for without some degree of control of every operation we could produce no steel worthy of the name. Although grouped together in this paper, insulation and control in open-hearth furnaces have little, if any, interrelationship, therefore the paper is made up of two distinct parts. INSULATION OF OPEN-HEARTH FURNACES More than ten years ago the writer proposed the insulation of an acid open-hearth furnace system below the charging floor, and it was accomplished, with gratifying results. Possibly that was the first time the insulation of regenerators and slag pockets of any open-hearth furnace was undertaken, but shortly thereafter such insulation became general, and when the six groups of 150-ton furnaces1 were built in 1929-1930, they were completely insulated below the charging floor. While the practice was accepted at least five years ago, it was not well understood, however, as indicated by the following incident which occurred in connection with an installation made in 1929. After the

Jan 1, 1935

By Francis Crockard

DURING the past five years we have probably witnessed greater technological advances than in any similar period. Industry and science have steadily marched ahead. The makers of iron and steel products have watched with great interest the development of stream-lined trains, faster and safer airplanes, the entirely new science of air-conditioning and the widespread use of stainless steels. Since 1930, we have witnessed the erection of the world's largest suspension bridge, the largest and fastest ocean liner and the spectacular Boulder Dam, while even greater things are planned in these particular fields. Other indus-tries, too, have been moving ahead rapidly. This advance in a few years has been caused primarily by the fierce competition of the depression. Now, more than ever, is the emphasis placed upon quality and service. Makers of southern merchant pig iron have been no exception and have been confronted with increasingly strict chemical specifications and with much greater stress on physical characteristics than ever before. For example, sulfur in the iron must be held very low, competition demanding that it be in the 0.020's and low 0.030's; silicon content must be held within a very narrow range, and definite requirements of phos-phorus and manganese are an essential part of the specifications. Physical characteristics are becoming of increasingly greater impor-tance. The introduction of triple-skimmed, slow-cooled iron several years ago was the first step in this direction. Now there are a few customers who buy iron by chemical analysis and physical appear-ance, having found that the analysis alone is an insufficient guide to their requirements.

Jan 1, 1935

By Calvin Pierson, R. S. Dean, E. P. Barrett

MANY studies have been made of the properties of steel produced by adding varying amounts of sponge iron to the charges used in steelmaking furnaces.1-3 The results of these previous studies, however, have failed to disclose a reason for the belief of steelmakers that steel made in this way is definitely different from steel made entirely from scrap or iron melting stock. This paper deals chiefly with the structure of the sponge iron, of the wrought iron made by welding the sponge iron into blooms, and of the steel made by melting the forged and rolled blooms. It is believed that the structure of the final steel is inherited from the ore and that this inherited structure produces marked differences in the properties of the steel and explains the feeling of steelmakers which is based on their experience. Three kinds of sponge iron were used in this investigation: One made from a limonite ore reduced with natural gas, one made from a hematite ore reduced with natural gas, and one made from a magnetite ore reduced with charcoal. The sponge iron made by reduction with natural gas

Jan 1, 1935

By Walter E. Duncan, Oscar F. Tangel, A. M. Gaudin, Franklin Dewey, R. A. Johnson

Xanthates have been used as collectors of sulfide minerals in the concentration of ores by flotation for over a decade, yet much remains to be done to elucidate the underlying reasons for the remarkable effectiveness of these compounds in this connection. Briefly stated, the known facts concerning the effect of these reagents on the floatability of minerals are as follows: 1. Xanthates are without effect on silicates, silica, and generally on minerals currently regarded as "gangues." 2. Xanthates in very small amount increase enormously the floatability of sulfides of copper, lead, silver, iron and mercury. 3. If zinc sulfides are first '(activated," as by treatment with a copper salt, they are readily floated by xanthates; otherwise not. 4. Elemental copper, silver and gold have their floatabilities increased by xanthates. 5. Sulfides of elements that are not typically metallic—e.g., stibnite, realgar, molybdenit—are not made to float markedly better by treatment with xanthates. 6. Oxidized minerals of lead and copper are floated if treated with large amounts of xanthates, but not so if treated with amounts of the same order of magnitude as required for sulfide flotation. Oxidized zinc minerals are not floated unless xanthates having unusually long hydrocarbon chains (e.g., eight carbon atoms or more) are used. Iron oxides and carbonate are not floated by xanthates. From a flotation standpoint the most striking feature about xanthates is the very small amount required to accomplish startling changes in the behavior of some minerals. The amounts used in practice to effect excellent concentration are frequently of the order of 0.05 lb, of agent per ton of ore; that is, of the order of one part of agent per forty thousand parts of ore. Changes in amount of agent of the order of 0.01 lb. per ton of ore (or 0.002 lb. per ton of pulp, on a 4:l basis) have marked effects on the metallurgical results obtained. Yet these changes represent a variation of but one part per million parts of pulp.

Jan 1, 1935

By Walter Miller

The broad picture of petroleum refining engineering during 1934 continued to show a tendency in the direction of highly specialized processing improvements, particularly in manufacture of lubricating oil. The slowing up of the trend toward higher octane products in non-premium gasoline noticed in 1933 was definitely established as a fact by 1934 development, with just a slight indication of recession. No outstanding engineering achievements can be credited to 1934 in refinery cracking, unless the completion and successful operation of the 30,000-bbl. crude capacity combination cracking and skimming unit at Texas City, Texas, and a 20,000-bbl. similar unit in the East can be listed as such. Development and improvement was largely a continuation of previous lines of endeavor. Such trend as there is shows a continnation in the direction of very large integrated skimming and cracking units. A lessening of the cost of ethyl lead, coupled with the reaching of the octane number "ceiling," kept the subject of "reforming" low-octane gasoline into high-octane products pretty well in the background. Considerable interest, however, was shown during the year in cracking and polymerizing of refinery gases into high-octane motor fuel. The commercial development and application of this activity was greater in 1934 than during any previous year. Fair yields of gasoline of satisfactory stability and high antiknock value were reported, ranging from 2 to 8 gal. per 1000 cu. ft. of fixed refinery gas, yields varying with both the nature of refinery gas treated and processing methods. Assuming economic feasibility, regarding which there is still difference of opinion, gas polymerization offers the industry a possible outlet for its gases more in keeping with its basic chemical composition and value. The increased interest of railroads and heavy-duty truck and tractor manufacturers served to focus more attention on diesel fuels. The publicity given the Union Pacific diesel train, the Burlington "Zephyr" and others operated on special diesel fuels served to revive the intimations and fears of several years ago as to the ultimate replacement of the gasoline motor by diesel engines in even the passenger car field. How-

Jan 1, 1935

By J. T. Eash, E. M. Wise

Platinum and palladium are the most generally useful, most ductile and least rare members of the platinum family. They have many important applications in the pure state but for other applications it is frequently desirable to harden them and otherwise modify their properties by alloying small amounts of the other platinum group metals with them. These alloys are frequently required to withstand very drastic forming operations and to possess certain mechanical properties to fulfill specific requirements. For these reasons a knowledge of the tensile properties and annealing characteristics of pure platinum and palladium as well as their more useful commercial alloys is important to the user and the fabricator. The present work was undertaken to fill this need. Rather brief (5 min.) annealing treatments were employed to render the data of maximum practical value and all tests were conducted upon 0.050-in. dia. wire, initially reduced 50 per cent in area by cold drawing, for the same reason. Conclusions 1. Pure (thermocouple grade) platinum reduced 50 per. cent by cold drawing exhibits the following tensile properties: ultimate tensile strength, 36,000 lb. per sq. in.; proportional limit, 27,000 lb. per sq. in.; elongation, 2.5 per cent in 2 in.; reduction in area, 95 per cent. When fully annealed by treatment at 1100°C. its properties are: ultimate tensile strength, 20,700 lb. per sq. in.; elongation, 30 per cent in 2 in.; reduction in area, 93 per cent. 2. The addition of alloying elements in moderate amounts markedly increases the strength and annealing temperature without much detriment to the ductility. The behavior and properties of variously hardened platinum alloys are considered in some detail. The behavior of a 20 per cent iridium

Jan 1, 1935

By Donald F. Irwin

Amid the violent economic changes of recent years that have affected Canadian gold-mining operations so deeply, the discovery and early developments of Kirkland Lake might easily be overlooked. There was more than one "false dawn" for the district before developments finally established the fact of a superb mineralized zone extending through the present operating properties. Never far from the railway, Kirkland Lake has had the benefit of direct rail service for many years. The pioneer discovery on which the first mill and cyanide plant was erected was the "Tough-Oakes," this property being on what is now the eastern end of the producing area; some time later, the "Lake Shore" was discovered at the present center of the district, and a small plant was built upon it also. Both of these early treatment plants were of pre-war design. Progress in gold metallurgy has caused a gradual change in cyanide practice since the early days at Kirkland Lake, which may be observed in the various plants now operating there. From the beginning, it was recognized that Kirkland Lake ores were more responsive to cyanidation than to alternative recovery methods, and that their mineralization contained gold in very finely divided form. Although sulfides and tellurides are present, the quantity is small, being in the order of 1 or 2 per cent by weight, so that gravity concentration is undesirable, since gold is not confined to the sulfides. Some complication is offered by the presence of tellurides, which have caused lengthy controversy over their importance in recovery methods, but which are now generally regarded as less harmful in the light of increasingly high recoveries being obtained. Nevertheless, finely divided gold intimately associated with sulfides in the presence of tellurides; and occurring in the hard Kirkland Lake porphyry ore, substantially free from natural slime-forming constituents, indicates fine grinding. This has been the universal practice although the degree of grinding has varied a little among the different mills and is considerably finer now than formerly. The natural condition as outlined caused the establishment of fine grinding at an early stage in the development of Kirkland Lake, during the period of valuation of gold at, $20.67 per ounce. With the arrival

Jan 1, 1935

By Harwick Johnson, E. W. Schilling

THE separation of hematite by hysteretic repulsion was first brought to the attention of the public in 1922, by W. M. Mordey1. Three years later another paper2 was published and after another four years a third paper3 appeared in the South African publications. Certain data were lacking in these papers. In order to continue the work intelligently a knowledge of the shapes of the hysteresis curves for certain minerals was very necessary. This information was not available until the present year4. It was known that reduction of certain ores rendered them amenable to this process of separation but definite data in the form of curves showing exactly the effect of such treatment were lacking. Probably our best source of information on the separation of minerals by the use of alternating-current magnetic fields today is the reports from the U. S. Bureau of Mines5-7. It is not the purpose of this paper to tell the reader in detail how to make a commercial separator. Experimental models have recently been made7 and the results obtained have been so good that it is the opinion of the authors that the public will soon take an active interest in the subject and its development. The writers have constructed a separator that is considerably different in construction and operation from the two types described by Mr. Davis. This will be described, but the real purpose of this paper is to outline certain experiments and give curves showing data that have a fundamental bearing upon the practical construction of a separator of this type.

Jan 1, 1935

By L. L. Foley, C. V. Millikan

The discovery of Bromide production in the Fitts field, shallow production in Jackson County of Southwestern Oklahoma, abundant production in the Edmond field, and discovery of many small pools in all parts of the state, were the events that made petroleum history in Oklahoma in 1934. Wildcatting was much more active, as evidenced by a number of new discoveries. There was no important development in the older fields. The rapid decline of the potential of the Oklahoma City field was an important feature of the history of the year. The accompanying tabulation of oil fields (Table 1) is not complete. Many of the early records of operators and pipe line companies are lost and it will be impossible to work up complete statistics for a number of the older fields. The table includes most of the important fields of the state and includes fields of a number of different types. It is hoped that a great many additional fields may be worked up for next year's report. Fitts Pool.—The Fitts pool, in Pontotoc County, was discovered in 1933. Before the middle of 1934, the Pennsylvanian sands yielded -some oil at depths ranging from 1400 to 2800 ft. The Hunton series (Siluro-Devonian) produced most of the oil with considerable gas. In July, 1934, a well in sec. 25, T.2N., R.6E. was completed in the Bromide (Ordovician " Wilcox ") with an initial production of about 300 bbl. a day. Less than a month later a second Bromide sand well was completed in sec. 30, T.2N., R.7E., which made over 200 bbl. an hour. This started an active drilling campaign, which was accelerated when some of the major companies paid good prices for adjacent acreage. At the end of the year, 23 wells had been completed and the rate of development was increasing rapidly. It is a major oil field. The Fitts pool opened a new geological province for oil production. The structure is a faulted anticline in a graben. The producing formation (Bromide) and the Arbuckle lime below it crop out about 2 miles south of present production. The Hunton lime crops out about 2½ miles north. The field is in a sharply folded and faulted area on the northeast side of the Arbuckle uplift. Heretofore, it was generally considered not favorable for oil production, although some gas had been found in various places. The play has extended east into the McAlester coal basin, and southeast toward the

Jan 1, 1935

By Albert Zima

ACCORDING to recently published statistics, it is predicted that as much oil must be produced during the next 16 years as has been produced during the past 75, in order to satisfy the high rate of consumption of petroleum products. During 1934, over 17,000 oil wells were completed in the United States, and it is expected that over 20,000 additional wells will be drilled during the current year. Were it not for the remarkable progress made during recent years in the improvement of drilling technique and in the development of equipment used in the production phase of the oil industry, it is doubtful whether sufficient oil could be produced to meet present requirements. A few years ago, wells seldom were deeper than 3500 to 4000 ft., owing to the limitations of the drilling methods and equipment employed. Today, however, through the application of scientific drilling methods and the adaptation of modern equipment and improved materials, many wells range from 6000 to 8000 ft, in depth, and a few recent completions exceed 10,000 feet.

Jan 1, 1935

By Clair Upthegrove, Elbert S. Rowland

THE widespread interest in the alloys of beryllium with copper is due principally to the fact that certain compositions show very favorable precipitation-hardening characteristics and are, in fact, the strongest nonferrous alloys known at the present time. Investigations have been conducted by Masing and Dahl and others on the physical characteristics of ternary beryllium alloys, in an attempt to produce precipitation-hardening effects with a smaller amount of beryllium than that required in the binary copper-beryllium alloys (2.0 to 2.5 per cent Be). The results of these investigations show that ternary alloys of beryllium with Cu-Sn, Cu-Al and Cu-Zn, among others, exhibit promising improvements in physical properties after precipitation-hardening treatment and, while the increases in properties obtained are not as high as those realized from the binary copper-beryllium alloys, excellent properties are: obtained with beryllium contents averaging about one-half the amount required in the binary alloys. This paper presents the results of an investigation of the equilibrium relations of certain alloys containing copper, tin and beryllium. The alpha-phase boundary of the ternary system is given for alloys containing from. 0 to 1 per cent beryllium. The equilibrium conditions beyond the alpha-phase boundary are presented for alloys containing up to 32 per cent tin and 1 per cent beryllium. The data were collected by means of

Jan 1, 1935

By J. W. Littleford

The Roan Antelope Copper Mines Ltd. are situated in the north central part of Northern Rhodesia, at an altitude of 4000 ft. and 13" south of the Equator. The town site (Luanshya) is well situated and enjoys among other things a really temperate climate for 10 months of the year. The two spring and summer months, October and November, while hot and humid, do not bring any great discomforts as compared with many other mining camps. Strictly modern brick homes, with electric lights, purified water, telephone and water-borne sewage, add to the comfort of the employees. A rainfall of approximately 60 in. per year furnishes ample water for both industrial and domestic purposes. The rainy season generally begins in October and lasts through until March. As much as 3 to 4 in. is recorded in 24 hr., but this offers no difficulties because the runoff is very rapid. The property is connected by a 24-mile branch line from Ndola with the main line of the Beira-Mashonaland and Rhodesia Railways Ltd. Practically all supplies from overseas are transported over this line from Beira, 1743 miles distant on the east coast in Portuguese East Africa. The mine output also leaves Africa from this port. Passenger service is principally via Cape Town or Durban, a distance of about 2100 miles to either port. The Imperial Airways maintain a service from Cape Town to Croydon, taking 9 days for the trip. Connections can be made with this service at Broken Hill, 150 miles south of Luanshya, by either rail or automobile. Thus, after several days of travel through virgin bush, a visitor arrives at a typically modern town site in the heart of Africa. Every development in mining, milling and smelting practice is used to advantage. Plan of Mill The practice in the three principal phases of the production of copper from the ores of this company have been published from time to time. Milling practice, however, is continually changing and what may be

Jan 1, 1935

World Petroleum Consumption. By V. R. GARFIAS AND R. V. WHETSEL. (Trans, vol 107). A tabulation showing world consumption of gasoline, kerosene, gas and fuel oil, lubricants, and miscellaneous petroleum products by counties in the years 1931, 1932 and 1933 , Totals are given; for instance, Cuba consumed 3,998,000 bbl of all petroleum products in 1933, in 1933; the world consumed 1,366,291,000 bbl. of all petroleum products, etc. Domestic Production. Annual Symposium of Petroleum Division, February Meeting, 1934 (Trans, vol. 107. 181 pages.) The symposium consists of reports on petroleum and gas developments and production in the producing states of the United States. This year the statistical information is presented in a new and far more comprehensive form. The reports on domestic production are as follows: Arkansas, by B C Craft; California, by V H. Wilhelm and H. W. Miller, Colorado, by C. E. Shoenfelt, Illinois, by A H Bell, Indiana, by W. N Logan and P. Simpson; Kansas, by Marvin Lee; Kentucky, Ohio and West Virginia, by V. C Smith; Louisi¬ana, by B C Craft, Michigan, by Theron Wasson; Mississippi, by B C Craft; Missouri, by F C Greene, Montana, by H. N Hickey, New Mexico, by C. E Shoen¬felt and D E Winchester, New York, by D. H. Newland, Oklahoma, by L. G. E. Bignell, J 0 Lewis and E. A Hanson, Pennsylvania, by G H Fancher, Tennessee, by L. C Glenn, Central Texas, by R B. Kelly and P R Martin, East Texas, by A R. Denison, Gulf Coast, by L P Teas, North Texas, by H B Fuqua and B. E Thomp¬son; North Central Texas, by J M. Armstrong, Panhandle, by R H Lynn and T. C. Craig, Southwest Texas, by 0. G. Bell; West Texas, by C W. Reith, Utah, by E S Shaw, Wyoming, by J G Bartram.

Jan 1, 1935

By James Paul

BEGINNING in December, 1933, and continuing to the close of April, 1934, large sums of money were expended in the states of Pennsylvania, Ohio and West Virginia through the conduct of Federal and State Civil Works Administration, financed by the Government as a part of the President's recovery program to furnish employment to mine employees idle as a result of the economic depression. PURPOSE OF THE PROJECT The protection of the public health against the pollution of public water supply by acid mine drainage was the incentive that prompted the request that the sealing of abandoned bituminous coal mines be made a Federal project. A paper before the Central Section of the American Water Works Association, Wheeling, W. Va., on Aug. 24, by E. S. Tisdale, Chief Engineer of the West Virginia Department of Health, tersely says: In October, 1933, the combined experience of the U. S. Bureau of Mines and the U. S. Public Health Service and the States of Pennsylvania, Ohio, West Virginia and Kentucky resulted in a report being filed in Washington, first with the Public Works Administration and later with the Civil Works Administration, where it was favorably acted upon, calling for these governmental agencies under the direction of the U. S. Public Health Service to expend $1,500,000 in a unified effort to seal abandoned coal mines in Pennsylvania, Ohio, West Virginia, Kentucky and six other states farther down along the Ohio river. The report referred to was embodied in a petition that was signed by the chief engineers of the State Departments of Health of the several states contiguous to the drainage area of the Ohio River. The project as established under Federal supervision became interstate with respect to the several states involved, and upon the termination of the Federal project on Feb. 15, it was authorized as a State C.W.A. project, effective Feb. 20, under the supervision of the State Departments of Health and the State C.W.A. Administration, which continued to March 29, and was succeeded by the S.E.R.B. of the R.W.D. from April 2 to April

Jan 1, 1935

By Benjamin N. Webber

Many of the auriferous placers of the arid Southwest differ widely from the standard types of stream and eluvial deposits of more humid regions, although exhibiting some of the features of each. This divergence in characteristics is of geological and economic importance and appears sufficient to warrant the consideration of these placers as a class distinct from both stream and eluvial deposits. It is hoped that the consideration of these auriferous gravels as a distinct type of deposit will facilitate recognition of morphological and economic features that might remain obscure if these deposits were viewed in the light of stream or eluvial placers whose type locality is a more humid environment. "Bajada placer" is proposed as the designation for this type of placer deposit. Bajada is the Spanish term for slope and is used locally in the Southwest to indicate the lower slope of a mountain range, the portion consisting of rock debris and standing at a much lower angle than the rock slope of the range proper. It has been used in a geologic sense by Schraderl and others. The type locality of bajada placers is the Sonoran Desert,2 where they occur on the bajada or rock debris slope of desert ranges. Stream placers are represented in the Southwest, but most of them lie within the mountain topographic province, the Mexican Highlands2 section of the Basin and Range physiographic province. Eluvial placers may occur in the mountainous semiarid Mexican Highlands but are almost unknown in the extremely arid Sonoran Desert, as mountain slopes are generally too steep to permit the accumulation of any considerable mantle of residual debris. Since their salient distinctions are almost wholly the result of formation under conditions of extreme aridity, bajada placers are largely confined to the Sonoran Desert, although a few occur in the adjacent Mexican Highlands. They may be modified by the action of ephemeral streams, in which case the placer gravels of these arroyos approach stream placers in type and habit of occurrence, but their relation to an arid environment and the bajada type is usually apparent.

Jan 1, 1935

By G. W. Jones

The determination of the ignition temperature of diethyl ether and ethylene in air and omen which is described in this report was made primarily for comparison with similar determinations of other compounds in the same apparatus and using the see laboratory technique. The investigation was conducted at the Pittsburgh Experiment Station of the United States Bureau of Mines with the cooperation of Merck & Co., Inc.

Jan 1, 1935

By E. D. Gardner

This paper discusses prospecting for lode gold and lists the principal lags and. regulations pertaining to locating; lode claims on public lands. It is a preprint of a part of a bulletin being prepared by the United States Bureau o Mines entitled "Equipping, Developing and Operating Small Gold Mines". The increased interest in gold mining manifested during the past few years (1932-1935) bas stimulated prospecting. Many adventurers have taken to the field to search for now gold deposits. A. large percentage of them have had no previous experience in prospecting for lode gold; this paper has been written with the tope that it might assist these newcomers.

Jan 1, 1935

By R. K. Hopkins

For a great many years fusion welding has been used in and around petroleum refineries, but it is only within six or seven years that the more important pressure vessels have been constructed by this process, because before that time the properties of fusion welds would not withstand such rigorous service. Since the adoption of fusion welding for the construction of this equipment, the refiner has required pressure vessels suitable for operation over a very wide range of conditions. On the one hand, vessels must operate at extremely high temperatures, in the range of 950" to 1000° F., and on the other vessels must be suitable for operation at sub-zero temperatures down as low as —75" F. Also, vessels are required suitable for operation at pressures upwards of 1000 lb. per sq. in., and as low as a 29-in. vacuum. In addition, vessels are required to withstand the attack of very corrosive mediums. It has been a rather difficult task for the fabricator to meet all of these requirements, but as a result of the extensive research carried on by steel manufacturers and several fabricators of class I vessels, practically all of these demands have been met. In order to meet the refiners' requirements for this wide range of conditions, the fabricator has worked closely with the metallurgist. This has enabled him to choose the proper base metal for each service condition, but it has been the fabricator's problem to develop a welding rod and welding technique, as well as a heat-treatment, that would produce in the welded vessel characteristics in and around the weld comparable to those in the base metal. Where corrosion is not a serious problem, and where the operating temperatures are not too high, ordinary carbon steel has served very well. But, when corrosion is serious, and/or when the temperatures are either very high or very low, it is necessary to use some form of alloy steel to give satisfactory service. A great deal of credit is due to the members of the Boiler Code Committee and also to the members of the Joint A.P.I.-A.S.M.E. Committee, who have formulated codes that insure the safety of the

Jan 1, 1935

By Benjamin Miller

FROM earliest recorded times, limestone has been employed in the industrial life of peoples of all sections of the world where it exists. It is widely distributed and therefore has been available in almost every country and has been employed for a variety of purposes. Its earliest use was for buildings, since it is more easily quarried and dressed than most other kinds of rocks and so could be utilized by early inhabitants, poorly equipped with tools. The next use was in the manufacture of lime, which was employed by the ancients in mortar. These two uses of limestone are still all important, but they have been overshadowed in scores of regions by literally hundreds of new applications for raw lime-stone or products made from it. Anyone familiar with modern manufacturing processes can quickly call to mind many industries in which limestones are essential, and new uses are continually coming to notice. Any enumeration would probably be incomplete and soon out of date.

Jan 1, 1935

By Plato Malozemoff, A. M. Gaudin

IN modern practice the major portion of an ore is reduced to flotation size by fine grinding. As the result of grinding fine enough to liberate most of the minerals, a substantial portion (generally 5 to 15 per cent) of the ore is inadvertently reduced to a size much finer than that necessary for liberation. This portion of most flotation pulps is very refractory to recovery by flotation. A reduction of one-quarter or more in recovery in this range of extremely fine particles can be observed. The loss in metals caused by overgrinding is appreciable. That this loss is characteristic of very fine particles has been suspected for some time;(l)† however, it was definitely quantified only recently.(2) Definite reduction in float-ability with reduction in particle size beyond a critical size of maximum floatability can be accepted now as an established fact. Formulating the Hypothesis In looking for the cause of the ill behavior of the finest particles it may be well to consider the essential differences between fine and coarse particles. A difference that immediately comes to mind is their intrinsic difference in size and consequently in relative extent of surface. If one agrees that attachment of mineral particles to bubbles must follow direct encounter of particles with bubbles one is forced to conclude(3) that the probability of encounter between a mineral particle and a bubble varies directly as the size of the particle, provided the particle is small compared to the bubble. In other words, the finer the particle the poorer its chance of being recovered in a given time of flotation. There is an effect, implicit in this theory, which should overcome the effect of excessive fineness of the particles; namely, flocculation of the particles. The floccules can be conceived as being simply larger particles and therefore capable of becoming attached to bubbles. And, indeed, in all the cases in which a sulfide mineral of near-colloidal size was successfully floated the mineral (but not necessarily the gangue) was flocculated. Moreover, it was shown experimentally(4) that galena previously flocculated by inorganic flocculators and then added to gangue

Jan 1, 1935