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By G. F. Loughlin

Nearly 55 years have elapsed since the U. S. Geological Survey was organized. During this period the mineral industries have grown from infancy or early childhood to well developed maturity, and some mining industries appear to be declining. Decline in mining is even more conspicuous in certain districts, or even states, than in any mining industry as a whole, and discoveries or developments of important new districts have been very few in recent years. Our reserves of most metals and nonmetals are adequate for many years of normal production, subject to changes in rate of exploitation that may be caused by foreign competition and by changes in technology and market conditions; but the declining production of many districts and the scarcity of important new discoveries to compensate for them is cause for some apprehension. It is likely that future production will depend to a considerable extent on deep exploration and on the thorough examination of places in and adjoining existing districts where significant outcrops are lacking and only apparently insignificant geologic features offer encouraging clues—more so than on the discovery of entirely new districts. Even the possible discovery of new districts, which have escaped the intensive search by the nontechnical prospector, must be dependent on geologic information. There is therefore no need for argument as to the value of geology to the mining industry; and the need of continuing to advance the science. The U. S. Geological Survey's past contributions to mining geology, as expressed in its official reports and other publications, are recognized by Ransome in his historical review of mining geology in the Lindgren volume.' These contributions have helped to form the basis of modern mining geology, which has grown rapidly in the last 25 years. This growth has witnessed the organization and maintenance of geologic staffs by mining companies in several districts, and their detailed work, together with the fact that nearly all of the larger mining districts have

Jan 1, 1935

By G. F. Loughlin

Nearly 55 years have elapsed since the U. S. Geological Survey was organized. During this period the mineral industries have grown from infancy or early childhood to well developed maturity, and some mining industries appear to be declining. Decline in mining is even more conspicuous in certain districts, or even states, than in any mining industry as a whole, and discoveries or developments of important new districts have been very few in recent years. Our reserves of most metals and nonmetals are adequate for many years of normal production, subject to changes in rate of exploitation that may be caused by foreign competition and by changes in technology and market conditions; but the declining production of many districts and the scarcity of important new discoveries to compensate for them is cause for some apprehension. It is likely that future production will depend to a considerable extent on deep exploration and on the thorough examination of places in and adjoining existing districts where significant outcrops are lacking and only apparently insignificant geologic features offer encouraging clues—more so than on the discovery of entirely new districts. Even the possible discovery of new districts, which have escaped the intensive search by the nontechnical prospector, must be dependent on geologic information. There is therefore no need for argument as to the value of geology to the mining industry; and the need of continuing to advance the science. The U. S. Geological Survey's past contributions to mining geology, as expressed in its official reports and other publications, are recognized by Ransome in his historical review of mining geology in the Lindgren volume.' These contributions have helped to form the basis of modern mining geology, which has grown rapidly in the last 25 years. This growth has witnessed the organization and maintenance of geologic staffs by mining companies in several districts, and their detailed work, together with the fact that nearly all of the larger mining districts have

Jan 1, 1935

By William M. Agar

Now that both the national and state legislatures are seeking ways of reducing expenses, the appropriations for geological investigation and for the study of mineral resources have been greatly reduced and in some cases entirely stopped. Is this policy justified? The sums saved by these reductions are always small. If the work accomplished by these surveys has no intrinsic value to the community, but is only an interesting way of spending some of the people's money when that money is plentiful, there should be no surveys at any time. If, on the other hand, they perform a necessary function, it is indeed foolish and short-sighted to save these paltry sums to the detriment of the community. It is not my purpose to undertake a general justification of geological surveys. Rather, 1 wish to call attention to the work of one state survey that has been discontinued, and to indicate ways in which the work was valuable to the people, even though that state's mineral resources are not very important, and why it should be continued. Though at one time in Connecticut's history iron mining and smelting were important, and copper was mined in appreciable quantities in two localities, it is many years since it could be regarded as a mining state. At present Connecticut stands far down among the states in the value of its mineral products. Granite for architectural and structural purposes, trap rock, clay, agricultural lime, feldspar and quartz, together with a few other nonmetallic minerals, are produced in appreciable quantities, but the natural resources of the state consist at present much more largely in its attractive scenery, woods, lakes, shore line, and in the opportunities that these offer for rest and recreation. Is the prosecution of geological work in such a state a waste of the taxpayer's money? Or can it be that though it was formerly valuable, the work is now completed? The only way to answer these questions is to review the geological work done in the past and to consider the type of information the people want, as reflected in the requests that have been received by the director of the survey in the last few years. There have been two periods during which Connecticut has supported geological work within its borders. The first began in 1835 when Percival

Jan 1, 1935

By William M. Agar

Now that both the national and state legislatures are seeking ways of reducing expenses, the appropriations for geological investigation and for the study of mineral resources have been greatly reduced and in some cases entirely stopped. Is this policy justified? The sums saved by these reductions are always small. If the work accomplished by these surveys has no intrinsic value to the community, but is only an interesting way of spending some of the people's money when that money is plentiful, there should be no surveys at any time. If, on the other hand, they perform a necessary function, it is indeed foolish and short-sighted to save these paltry sums to the detriment of the community. It is not my purpose to undertake a general justification of geological surveys. Rather, 1 wish to call attention to the work of one state survey that has been discontinued, and to indicate ways in which the work was valuable to the people, even though that state's mineral resources are not very important, and why it should be continued. Though at one time in Connecticut's history iron mining and smelting were important, and copper was mined in appreciable quantities in two localities, it is many years since it could be regarded as a mining state. At present Connecticut stands far down among the states in the value of its mineral products. Granite for architectural and structural purposes, trap rock, clay, agricultural lime, feldspar and quartz, together with a few other nonmetallic minerals, are produced in appreciable quantities, but the natural resources of the state consist at present much more largely in its attractive scenery, woods, lakes, shore line, and in the opportunities that these offer for rest and recreation. Is the prosecution of geological work in such a state a waste of the taxpayer's money? Or can it be that though it was formerly valuable, the work is now completed? The only way to answer these questions is to review the geological work done in the past and to consider the type of information the people want, as reflected in the requests that have been received by the director of the survey in the last few years. There have been two periods during which Connecticut has supported geological work within its borders. The first began in 1835 when Percival

Jan 1, 1935

By Hugh M. Roberts

The important place in the economic life of the country that is occupied by the United States Geological Survey and the various state surveys is appreciatcd by most members of our Institute. To the public at large, the functions of these surveys are no doubt largely unknown, and taken for granted. Possibly a realization of the value of the work of these government branches is brought home most fully to that group of our members whose duties as examining engineers and mining geologists take them to mines and prospects in many different parts. The examining engineer or geologist is usually seeking for a judgment on the value of an enterprise from the standpoint of the useful minerals that may or may not be present; he must also attempt some prediction as to future market prices. On his opinion rests the determination of the expenditure of money, which rendered into other language means the expenditure of human effort. An opinion on an exploring venture or the reasoning out of the probable extensions of an orebody requires among many other things a background of knowledge covering the geologic horizons not only of an immediate area but of the surrounding area, a knowledge of the structural geology and of the causes that have operated to form the ores as they are. The great storehouses of this knowledge are the statistics, reports and maps issued by the various geological surveys. They supply the groundwork for additional observations. To these, reference is always made when going into a new district. The technique of work in the field and laboratory, and to some extent the hypotheses that underlie our methods of approach, have been formed by men such as Van Hise, Leith, Kemp, Spurr, Emmons and Lindgren, who developed their powers in the service of the geological surveys. In addition to whatever originality of thought, or power to observe facts and analyze them, may be our portion, we require, in the application of the arts and sciences, a knowledge of what has already been done. We stand on the shoulders of those who have gone before, and the extent of our vision often depends upon the thoroughness with which we form earlier work into one whole and make use of it.

Jan 1, 1935

By Hugh M. Roberts

The important place in the economic life of the country that is occupied by the United States Geological Survey and the various state surveys is appreciatcd by most members of our Institute. To the public at large, the functions of these surveys are no doubt largely unknown, and taken for granted. Possibly a realization of the value of the work of these government branches is brought home most fully to that group of our members whose duties as examining engineers and mining geologists take them to mines and prospects in many different parts. The examining engineer or geologist is usually seeking for a judgment on the value of an enterprise from the standpoint of the useful minerals that may or may not be present; he must also attempt some prediction as to future market prices. On his opinion rests the determination of the expenditure of money, which rendered into other language means the expenditure of human effort. An opinion on an exploring venture or the reasoning out of the probable extensions of an orebody requires among many other things a background of knowledge covering the geologic horizons not only of an immediate area but of the surrounding area, a knowledge of the structural geology and of the causes that have operated to form the ores as they are. The great storehouses of this knowledge are the statistics, reports and maps issued by the various geological surveys. They supply the groundwork for additional observations. To these, reference is always made when going into a new district. The technique of work in the field and laboratory, and to some extent the hypotheses that underlie our methods of approach, have been formed by men such as Van Hise, Leith, Kemp, Spurr, Emmons and Lindgren, who developed their powers in the service of the geological surveys. In addition to whatever originality of thought, or power to observe facts and analyze them, may be our portion, we require, in the application of the arts and sciences, a knowledge of what has already been done. We stand on the shoulders of those who have gone before, and the extent of our vision often depends upon the thoroughness with which we form earlier work into one whole and make use of it.

Jan 1, 1935

By F. W. McNair

WITHIN the last twenty-five or thirty years the actual operations of the great mining industry have passed almost wholly under the charge of men trained in the technical colleges. It follows that the industry is profoundly influenced for good or ill by the character of the training which the college graduate receives, and the relations existing between the industry and the colleges. This fact seems to be generally recognized, as evidenced, for example, by the existence of a Committee on Technical Education created some two or three years ago by the Mining and Metallurgical Society of America. In 1921 this committee rendered a very able and. extremely well poised reports of technical education as applied to the prospective mining engineer. It deserves the attention of every one interested in the effectiveness of engineering training. That the importance of the relation between the mining industry and the engineering colleges is recog-nized is evidenced also by the mass of criticism, usually adverse, which is proffered to and often hurled at the colleges by those in the industry. The man inn the field sometimes goes so far as to say that engineering educa-tion is hopelessly inefficient and its product worthless, while the college worker sometimes complains that the demands of the industrialist are too numerous and conflicting to be met, and adds that they would' best be ignored. Between these extremes, there seems to be a general consensus of opinion that the training of the would-be engineer can be, and. ought to be, made much better than it now is.

Jan 4, 1923

By C. W. MacGregor

IN the testing of materials there exist various methods of recording graphically the behavior of a material subjected to tensile stress. Prob-ably the most common method is to plot the tensile stress So, obtained by dividing the load P by the original area of cross section AO at the start of the test, as a function of the strain ?o, which is obtained by dividing the ?Lo or the change in the gauge length by the original gauge length Lo. A list of the symbols used here is given in Table 1. This method, while it has proved useful in the routine testing and comparison of various materials, does not have a very sound physical basis, as was first pointed out by P. Ludwik1, and consequently does not afford a very deep insight into the true physical behavior of the material under stress. Among the objections to this method may be mentioned: (1) that by dividing the load P at any stage of the test by the original area Ao a fictitious stress is obtained, which does not actually exist; (2) that the strain ?o = ?Lo /Lo is not an exact expression for the true strain for large values of ?Lo in per cent of Lo; (3) that when necking starts the strain varies considerably along the gauge length and the above expression no longer gives the true strain existing at any point on the outside of the bar; and (4) that the axial strain varies over the cross section of the necked portion and ?o does not represent an average of these strains over the cross section. Stresses taken from such a diagram would be only approximate and, if used to compare results of a test on a given material under simple tension with results obtained under combined stresses, certain errors would he thus introduced. In order to overcome some of these objections, various methods have been suggested, both as to the quantities to be measured and as to their graphical representation. In some cases the so-called "true stress," obtained by dividing the load P by the actual area of cross section A existing when the load P was applied, is plotted as a function of the strain

Jan 1, 1937

By Harold L. Lovell

The extensive heterogeneity of coal is a fact long recognized by scientists and engineers. However, until recent years the practical implications of such heterogeneity have more often been realized from an undesirable experience than from knowledge or forethought. Variations in the properties of coal, even within the same seam, eventually lead to procedural modifications in mining, handling, preparation and utilization. The concepts considered here propose an enhanced application of information, detailing these properties, realizing the uniqueness of any given coal seam but the practicality of a common approach. Coal preparation practice has been designed primarily for the control of ash and sulfur content to meet market specifications which are similarly specified, Other physical characteristics of size and friability are also commonly employed and, to a lesser extent, properties which are implications of rank. The consideration of petrographic data as indicators of origin, thus total physical and chemical properties, has generally been overlooked as a realistic tool in-the exploitation of coal as a resource. The evolution of descriptive techniques, whether petrographic, physical, or chemical, capable of universal application with any rank of coal, is still beset with problems.

Jan 1, 1968

At the University Club, New York, Jan. 23, Chairman George E. Hale and other officers of the National Research Council, gave a dinner to officers of the national engineering and other societies. About thirty persons were present, including officers of the National Research Council, the four Founder Societies, American Society for Testing Materials, Society of Automotive Engineers, Inc., Illuminating Engineering Society, United Engineering Society, and Engineering Foundation. Letters were received from the Western Society of Engineers, which also had been invited. Gano Dunn, vice-chairman of National Research Council, was toastmaster. The proposed permanent organization of the National Research Council and possible methods of connection with the national engineering societies, either directly or through Engineering Foundation, were outlined. It was suggested that not only the four Founder Societies be represented in the Engineering Division of National Research Council, but also that the other national engineering societies be admitted to membership. It was proposed that the Engineering Division should have a chairman who should be an engineer of wide reputation and of the highest professional attainments who should devote his whole time to the establishment and development of the Division. Methods of organizing industrial research were discussed. At a subsequent meeting of the National Research Council, an invitation was issued to each of the national societies to form a research committee encouraging that committee to become active in the promotion of research within its respective field. Due recognition is to be given each committee in the general organization of the National Research Council. Dr. H. M. Howe, in a very interesting and comprehensive address, told of much important work that had been clone by the various sections of the Research Council, as that of mechanical engineering in developing the often rather nebulous devices for helping win the war and putting them in such form that they could be of direct use to the military service. The section on metallurgy, till lately under Bradley Stoughton and now under G. H. Clevenger, did much valuable work in the improvement of helmets and body armor and made very extensive ballistic tests with refractory steels for this purpose. Important work was done in investigating the fatigue of metals and results of great moment were achieved. The committee on ferro-alloys, under J. E. Johnson, Jr., did important work in effecting economy of manganese in steel manufacture with a view to reducing the necessity for importation of manganese ore, thus releasing ships for other purposes. , The section on electric welding has accomplished valuable results in the development of electric welding for ships, a new branch of industry of very great promise.

Jan 3, 1919

By James P. Dr. Kimball

SULPHUR is always present in mineral coal of every variety. In the oxidized state it may exist as sulphuric acid in combination with a base. In the unoxidized state it exists in combination with iron as bisulphide of iron. It is also supposed by some chemists to exist in unknown combinations with the organic elements of the coal. This supposition requires the demonstration as a fact that certain coals yield more sulphur than what may exist in a free state, or what belongs to recognized combinations, not only with the accompanying iron but with other inorganic bases abundantly occurring in coals, but which unfortunately are very rarely estimated. This practically as well as theoretically important question it is at present impossible to decide, simply for want of available thorough ultimate coal analyses including the ash. Such analyses, at the best imperfect, are laborious and intricate, and therefore seldom made, the much simpler proximate analyses, so-called, being resorted to by most chemists for technical purposes, and commonly substituted for more scientific work even in the laboratories of government surveys. And it is unfortunate enough that few ultimate analyses are extended to the composition of the ash, much less to its relation to the original constitution of the coal. Sulphur chiefly occurs in most coals in the form of yellow pyrites (pyrite) and white pyrites (marcasite), both minerals, characterized by differences in crystalline form and in physical properties as well as in color, but having the same chemical composition (FeS2). No coal is entirely free from one or both of these dimorphous forms of bisulphide of iron. It may be disseminated through the mass so as to be invisible, in plates or scales between the laminæ of the coal, or in conspicuous segregations or nodules, sometimes of considerable dimensions. Coals greatly differ as to the proportion of sulphur which they contain. They also differ as to the relative proportion in which its several forms of combination occur. Such qualitative and quantitative disparities are scarcely, if at all, more marked in separate coal seams of a uniform type than in different parts of one and the same coal seam, whether it be considered locally as constituted of several

Jan 1, 1880

By W. H. Emmons

THIS paper is the third of a series treating of the relations of ores of the metals to igneous rocks. The first1 outlined the general problem; the second2 proposed a classification of lode ores, and showed how the distribution of the deposits is in a certain measure controlled by the contour of the roof of the parent batholith. A number of mining districts were discussed, the examples being selected chiefly from group 2 of the classification. The proposed classification of lode deposits, briefly stated, is as follows: 1. Cryptobatholithic: near hidden batholiths which have not yet been exhumed by erosion. 2. Acrobatholithic: in and near cupolas or domes of batholiths-the high points of larger underlying masses. 3. Epibatholithic: on batholiths, near their rims, but below eroded cupolas, or below the highest points of the roofs. 4. Embatholithic: among closely-spaced outcrops which probably are parts of a single batholith. The outcrops of invaded rocks predominate. 5. Endobatholithic: in and near roof pendants of large batholiths. The invading rocks predominate. 6. Hypobatholithic: in deeply-eroded batholiths, where even roof pendants, have been -eroded. Deposits of certain metals on the roofs of the batholiths are much more numerous in some positions than deposits of other metals, and the horizontal zonal arrangements of lodes of different metals are shown characteristically only in certain groups. In a large measure, also, the character of the fracturing and metallization is determined by, the-position on the roof, of the batholith.

Jan 1, 1927

By Persifor Frazer

AMONG the geological problems with which the present Pennsylvania Geological Survey has had to deal is the relative age of a series of strata passing around and through the city of Philadelphia, Bucks, Chester, and Delaware counties. Rogers includes all these rocks in his hypozoic series, and every student, so far as the writer knows, with one exception, has assigned to them a position beneath the Potsdam sandstone, or " Primal " of that eminent and gifted geologist. So far as regards the small portions of this belt, to which it is the intention of the present paper to draw attention, even the one geolo - * Read at the Lake Superior Meeting, August, 1880.

Jan 1, 1881

By Ralph Arnold

THE American oil 'industry has reached the critical stage where the demand exceeds the supply with no hope of permanently bettering the situation through the development of new fields in the United States. Remedies may be sought along three lines: 1. Securing a foreign source of supply. 2. Curtailment of the use of oil and its derivatives. 3. Improvement in methods of recovery (including the recovery of shale oil), refining, and utilization. The oil companies with proper government support will push the acquiring of foreign territory; the price of oil and oil products will enforce a curtailment in use; it remains for the producers and refiners to brings about improvements and economy in recovery, transportation and refining; the general public must be instructed in utilization. The solution of the problem, therefore, rests largely in the hands of the technologists of the industry -the drillers, engineers, geologists, chemists, etc. Only through an exchange of the ideas of the individuals who are conducting the industry will its technology be advanced. , Among the agencies at work to bring about this result are the United States Bureau of Mines, the American Petroleum Institute, and the A. I. M. E. The Bureau of Mines has a trained staff of experts, maintains experiment stations and a field force of technologists, and issues many technical papers helpful to the industry. The Petroleum Institute is a clearing house for useful statistics and is now. organizing a research division under the able direction of Doctor Manning, but its principal field of activities is in the realm of co¬ordinating ?the financial and commercial activities of the` oil' companies.' It remains for the American Institute of Mining and Metallurgical Engineers to organize the individual technologists of the industry and provide them with means of exchanging and disseminating ideas through meetings and publications. It is the aim of the Petroleum Committee of the American Institute of Mining and Metallurgical Engineers to foster this exchange of ideas among oil men by enlarging the membership of the Institute among the field and office technical forces of the oil companies and thus arouse their interest in the vital problems of the oil business.

Jan 1, 1920

By P. Bevilacqua, G. Ferrara

The paper discusses the problem of accuracy in the determination of the partition curve of gravity separation processes, which is strongly affected by both the sharpness of separation of the density analysis system used and the width of the density range selected. The problem is important when the density analysis of the separation products cannot be performed using heavy liquids, but has to be performed using heavy suspensions or using other systems such magnetogravimetric separation. The imperfect separation given by these systems and the use of large density ranges lead to the determination of apparent partition curves instead of actual partition curves for the process. In the paper the relation between apparent and actual partition curves is studied under different conditions through a simulation program. For different input data, special diagrams are given which, once the apparent partition curves and the sharpness of the density cuts are known, allow calculation of the actual partition curves and the related parameters.

Jan 1, 1995

By D. Richter

The Pyrometallurgical refining stage of ferronickel manufacturing produces a slag rich in iron and nickel, which is usually further processed for metal recovery. The recovered material is returned to the refining or smelting stages, depending on the amount of impurities. A series of tests was carried out on the Mineração Morro Azul refining slags, aiming at the recovery of the metallic particles through physical processing. Minor changes in the process showed improved results. This paper compares the textures of these slags after being cooled at ambient temperature and granulated under water at high pressure and flow. It concludes that the cooling process is intimately connected to the work index of such slags, thus resulting in direct impact in operating costs.

Jan 1, 2011

By İsmail İnce

The existence of water is one of the most effective factors in deterioration of natural building stones. In the process of deterioration, capillary water absorption is the most significant procedure of water penetration into the building stones. Pyroclastic rocks have been widely utilized as building stone especially in historical buildings and monuments since ancient times in the Central Anatolia in Turkey. Nowadays, this type of rocks is used in the restoration of historical buildings as well as in the construction of modern buildings. Pyroclastic rocks are highly susceptible to deterioration process. Capillary rise has a significant influence on water penetration into building stones. Therefore, it is quite important to identify the factors affecting the values of capillarity, capillary rising speed, and capillary rise that define capillary water absorption in these rocks. To this end, pyroclastic rock samples in different textures were compiled from the Cappadocia region, in Central Anatolia. First, petrographic, mineralogical, geochemical, physical, and pore diameter distribution properties of the samples were determined in the laboratory. Then, capillarity values with capillary rise and capillary rise speeds dependent on time were established. Based on the data obtained, correlation coefficients between matrix percentage and capillary water absorption rate and capillary rise values of pyroclastic rocks were calculated and found to be as 0.850 and 0.891, respectively. Thus, the article proposes a new empirical equation to practically calculate the capillary rise value depending on the matrix percentage (MP) and median pore diameter (MPD) values.

Nov 30, 2020

By Peng ZANG, Qihang Liu

Experimental work was conducted to determine the relationships of coal char conversion with temperature and heat absorption. The results show that at an earlier stage of the coke forming process, lump coal would absorb large amounts of heat but the increase of high temperature strength of lump coal was not significant. Contrarily, the lump coal’s high temperature strength was greatly improved at later stage of coke forming process. A number of residual coal was found in most tuyere coke samples illustrating that the lump coals added in the melter gasifier were not completely transformed into coke when they arrived at the tuyere region. The results indicate that the improvement of lump coal’s high temperature performance is limited in the melting gasifier by the low coke forming rate which could become the core factor of fines generation of lump coal in the melting gasifier.

Jan 1, 2016

IN all wet concentration processes it is of primary importance to determine to what degree the crushing must be carried in order to obtain the maximum profit per ton of ore milled.To effect a clean separation, either by gravity or flotation treatment, between either one valuable sulphide from another, or a sUlphide from the gangue, the ore must have been subjected to grinding to such an extent that the particles to be separated are completely liberated from each other.Insufficient crushing will result in either an incomplete separation of the sulphides from each other, and thus a loss of the one sulphide in the other, or else a loss of the valuable sulphide in the gangue.This being so, the question arises whether the added cost of extra crushing would be economically warranted by the increased recovery consequent on such a step.

Jan 1, 1927

By L. McWilliams, L. D. Patts, J. D. Noll, S. E. Mischler

Elemental carbon (EC) is currently used as a surrogate for diesel particulate matter (DPM) in underground mines since it can be accurately measured at low concentrations and diesels are the only source of submicrometer EC in underground mines. A disadvantage of using EC as a surrogate for DPM is that the fraction of EC in DPM is a function of various engine parameters and fuel formulations, etc. In order to evaluate how EC predicts DPM in the underground mining atmosphere, measurements of total carbon (TC; representing over 80% of the DPM) and EC were taken away from potential interferences in four underground metal/non-metal mines during actual production. In a controlled atmosphere, DPM mass, TC, and EC measurements were also collected while several different types of vehicles simulated production with and without different types of control technologies. When diesel particulate filters (DPFs) were not used, both studies showed that EC could be used to predict DPM mass or TC. The variability of the data started to increase at TC concentrations below 230, µg/m3 and was high (>+20%) at TC concentrations below 160 µg/m3, probably due to the problem with sampling organic carbon (OC) at these concentrations. It was also discovered that when certain DPFs were used, the relationship between DPM and EC changed at lower DPM concentrations.