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By H. Singh, Anupam Agrawal, H. S. Grewal

"Erosion in industrial appliances causes huge loss of valuable resources especially when solid particles are present in the working medium. A number of erosion models that are available in the literature claimed to predict the erosion response. In this work, five erosion models have been evaluated using computational fluid dynamics (CFD) methodology. Three most commonly used experimental test rigs (solid particle and unsubmerged slurry jet type and pot type) have been simulated and comparisons with the experimental results have been performed. The study helps in understanding the effect of fluid medium and flow pattern on the erosion process. The knowledge acquired shows that phenomenological based erosion models give better results considering the wide range of operating parameters. The in-depth study of the flow field shows the possibility that erosion mechanism, being parameter dependent, could change with location on the same specimen.1.0 IntroductionErosion is a surface degradation phenomenon which causes the removal of material due to impacts either of solid particles and/or bubbles or gas entrained in a fluid medium. Erosion has various categories depending upon the erosion medium such as, solid particles erosion (solid particles entrained in gaseous medium), slurry erosion (solid particles entrained in liquid medium) or cavitation erosion (erosion caused by exploding gas or vapor bubbles). Humphrey [1] has listed 21 different factors that decide the erosion response of the components under a given working condition. The number of factors involved in the erosion process gives us an idea about its complex nature."

Jan 1, 2012

Urban railway systems need high invest- ments, especially if their routes and stations have to be placed in the subsurface. In the FRG the construction and equipment cost of urban underground railway systems are in the range of 60 to 100 Mill DM per km tunnel. For this reason, track sections on the surface and on elevated structures are used as far as that is possible. Considering whole systems, the costs are in a range from to 45 Mill DM per km length for a metro system with about 80 % of its tracks and stations in tunnels and from 20 to 25 Mill DM per km for a light railway system with about 25 % subsurface infra= structure. The amount of route lengths in tunnels depends on the size of a city, the situation regarding above ground structure and free space on the surface, the level of service quality which has to be achieved with the railway system etc. Despite of the urgent needs to improve the transport conditions there very often arise doubts if an urban railway system is really necessary and can be justified in an economic sense. The experience from many cities around the world shows, that there arise a lot of benefits from urban railway systems, especially with larger sections placed under- ground. They are to be found in the interests of the operator (f.e. operating costs), the user (travel time, quality of service etc.) and regarding social aspects (environmental protection, accidents, consumption of energy Etc.).

Jan 1, 1987

By Leon Y. Sadler, E. K. Landis

Froth flotation has been described by several authors" as being analogous to a first-order rate process. Although a few investigators"," have found orders other than one fit their data best, the rate is described most often by the first-order equation, [ ] where r is rate of disappearance of floatable mineral by flotation, C(t) is concentration of floatable mineral in the cell, t is time, and k is first-order flotation rate constant. One of the difficulties in using this rate equation to develop a mathematical description of an actual flotation process is the determination of a suitable value of the constant k. The value of k, which reflects the floatability of the floatable mineral, is dependent on the hydrodynamic conditions in the cell, type and concentration of flotation reagents used, pulp density, and pH, method of froth removal, aeration rate, particle characteristics, and many other factors. Therefore, it is reasonable to expect that each particle of floatable material has a distinct value of k and that a unique distribution of k values exists for given feed and cell conditions. This has been observed and discussed by several investigators, and mathematical descriptions of the batch cell and steady-state continuous cell with distributed flotation rate constant have been developed." The mathematical description in the form of a transfer function of the continuous or flow cell under unsteady-state conditions with a distributed flotation rate constant has not been presented in the literature. The purpose of this note is to make such a presentation. The basic features of the perfectly mixed continuous

Jan 1, 1974

By J. Jolly

THIS short note on the probable character of the organic sulfur compounds in coal can do no more than indicate lines of research. We have no new experimental work to describe, nothing comparable in value with the careful studies of American coals by Powell and Parr1 and Yancey and Frazer.2 A study of the manner in which sulfur compounds exist in British coals (and their behavior on heat treatment) is rendered increasingly necessary by the fact that the British reserves of good coking coals of reasonably low sulfur content are fast being depleted. We believe that it is essentially by a study of the modes of formation, occurrence, and decomposition of the various types of inorganic and organic sulfur compounds in coal that it will be possible, with hope of success, to attack the problem of purifying coals, otherwise eminently suitable for coking, from these objectionable ingredients. Sulfur, so far as is at present known, does not normally occur in the free state in the coal conglomerate, but is chiefly distributed, irregularly, in three forms: 1. As primary constituents of the coal conglomerate, organic in nature and probably associated with those molecular complexes that have resulted from the degradation of the proteins of the plant tissues responsible for the formation of the coal mass. These constituents can be classed as "organic sulfur." 2. As metallic sulfides, e.g., iron pyrites. 3. As metallic sulfates, e.g., calcium sulfate and ferrous sulfate. (The occurrence of these compounds varies with the occurrence and degree of degradation of class 2.)

Jan 3, 1925

By A. Bumanis, K. S. Bawa

INTRODUCTION A rail rapid transit system called the "Metro" system is presently under construction in the Nation's Capital area. The agency responsible for the design and construction of the Metro system is the Washington Metropolitan Area Transit Authority, an independent tristate organization set up under an Act of Congress and financed by federal, state, and local public funds supplemented by revenue bonds. When completed, the Metro system will comprise nearly 100 route miles. About fifteen percent of this mileage is now under construction, while designs for the-remainder are in progress. The system is scheduled for completion in about eight years at a cost of approximately 3 billion dollars. The Metro system will involve nearly all types of construction generally used for rapid rail transit projects. About half of the mileage will be underground, comprising approximately 16 miles of rock tunnels, 10 miles of earth tunnels, and nearly 21 miles of cut-and-cover construction in earth (see Figure 1.). The remaining 51 miles of the system is planned to be constructed on the surface as at-grade or elevated structures. The system includes 86 passenger stations, 53 of which will be underground structures. Twelve of the underground stations will be large size chambers in rock while other underground stations will be constructed in earth as cut-and-cover structures. Thus, about one-fifth of the system will be designed as underground structures, namely tunnels and stations, in rock. Such designs in rock resulted from the existence of bedrock (schistose gneiss) at reasonable depths generally in the north and northwest

Jan 1, 1997

By Robert Maddin

crystal prior to, polishing in order to eliminate coring. This treatment may be accomplished by wrapping the single crystal tightly in very thin, dead soft, brass foil and annealing in the presence of air for 20 hr at 800°C. Since the wrapping encircles the sptcimen three to four times, only a very slight amount of oxidation occurs on the specimen surface. On unwrapping one of these cylindrical single crystals. in. in diam by ro in. long (72.75 pct cu, 27.23 pct Zn, 0.01 pct P11, 0.01 pct re), mall light-gray depnrrits in the form of circular arcs werenoted on the part nf the foil which had been in contact with the single crystal, Fig r. (By superim- approximatetl). These deposits, which, from their color, suggest the appearance of sublimated zinc, were found to coincide roughly with a set of octahedral planes nearly perpendicular to the rod axis. The pattern shorn in the figure held no relation to the profle of the sample since the markin~s on the crystal More annealing werc attributed to traces of cube planes. It seems very likely that the deposits were formed by sutllimation of zinc diffusing from octahrdral planes since diffusian would Eogically take place along planes of maximum atomic spacing. However, it is difficult to understand why a continuous sublimation of zinc should occur from a single crystat in contact with a wrapping roil OF the same composition, and why diffusion would take place along specific octahedral planes and in a regular pattern.

Jan 1, 1949

By C Rogers

"The Coal Seam Gas (CSG) industry has seen a rapid increase in activity over a 30-year periodfrom the early 1990s within Australia. Despite public concerns over environmental issues, theCSG industry has increased in Queensland to the point where more than 90 per cent of naturalgas consumed in Queensland is CSG. The New South Wales (NSW) CSG industry has been slowerto respond for many reasons. Ninety-five per cent of natural gas consumed in NSW comes frominterstate. However, CSG activity in New South Wales is increasing notwithstanding publicconcerns. The CSG potential of three Petroleum Exploration Licenses (PELs) are being assessedwithin the Southern Sydney Basin that provides a unique opportunity to develop resourcesstrategically around many abandoned coal mines. The question has been asked - what do theseabandoned coal mines mean to the project? Are they good or bad? Are they friend or foe? Thispaper att empts to answer these questions and in doing so describes the coal mine ventilation andgas management philosophies and practices used to assess gas production potential. The coalmining philosophies not only have the potential to assist in the construction of a highly successfulCSG project, but they also potentially add signifi cant pre production value by re defi ning how theresources and reserves are assessed and therefore valued. The behaviour of abandoned coal minesand the goaves within the PELs are not well understood by the petroleum industry. However, in the Illawarra region there is an abundance of coal mining knowledge and expertise that if properly focused can greatly increase the chances of project success."

Jun 1, 2012

By Maria I. De Rosa

Table 55 and figure 19 show the number of fires and fire injuries for stone mills by state during 1990-2001. Table 55 also shows the injury risk rates, employees' working hours, and lost workdays. In all, 118 fires occurred in 33 states. Seventy-six of the fires caused 82 injuries (including 8 fires and 6 injuries involving contractors). The yearly average was 9.8 fires and 6.8 injuries. The Ewhr value was 873 x 106 hr (In = 0.019), and the LWD value was 1,911. Missouri had the most fires (16 fires and 9 injuries), followed by Pennsylvania (15 fires and 14 injuries), Michigan (9 fires and 5 injuries), and Virginia (7 fires and 5 injuries). Of these states, Virginia had the highest injury risk rate value (In = 0.09 1). Table 56, partly illustrated in figure 20, shows the number of fires, fire injuries, risk rates, employees' working hours, and lost workdays by time period. The number of fires and fire injuries decreased during most of the periods, with a sharp increase during the last period. The number of employees' working hours increased throughout the periods. The In values follow patterns similar to those shown by the injury values. Tables 57-63 show the number of fires by ignition source, method of detection and suppression, equipment involved, location, and burning material by time period. Figure 21 shows the major variables related to fires for 1990-2001. Table 63 shows the fire injuries per number of fires causing injuries and total fires by year, ignition source, equipment involved, and location.

Jan 1, 2004

By R. V. Ramani, C. B. Manula, A. Owili-Eger

That a close analogy exists between the flow of air in mines and the flow of current in electrical networks- has been known for a long time. The laws that have been used to solve series and parallel electrical circuits have been used to solve for the equivalent resistance in mine ventilation problems. Kirchhoff's current and voltage laws have also been adopted in solving mine ventilation network problems. It will be best to define a few terms here regarding networks, and with reference to Figure 1, these definitions can be elucidated. Figure 1 can be represented by the network in Figure 2 without losing any essential details. 1. A junction is a point where two or more airways meet. 2. The segment of a roadway connecting any two junctions is known as a branch. 3. A mesh is a closed path through the network. In the above network, B, C, D and F are the junctions, CF and CD are two of the branches and CFDC is a mesh. Kirchhoff's current law states that the sum of currents entering a junction. Applying this law to the junctions in the ventilation network, one obtains for junctions C and F, the following relationships: JUNCTION C: Q1 = Q4 + Q3 (1) JUNCTION F: Q2 + Q3 = Q5 (2) Similar relationships can be drawn for other junctions. Kirchhoff's voltage law states that in any complete electric circuit, the algebraic sum of the emf's must equal the algebraic sum of the voltage drops. In mine ventilation, the square law (Atkinson's

Jan 1, 1975

By C. Dinis da Gama

In mining, all unit operations are closely interrelated, and the results of blasting are probably the key factor within that sequence. The drilling program prior to blasting is just as dependent upon the desired rock fragmentation as are the loading, hauling, and mechanical crushing operations which are economically and technically influenced by the results of blasting, namely, the size and scatter of the product. What is known today as optimum blasting is the process of designing a blast in order to obtain a certain degree of fragmentation so that overall mining costs are minimized. Applying this criterion often results in a different program than when an individual blasting pattern is chosen only on the basis of the lowest operational cost for that pattern, disregarding what comes before or after the blast. [Fig. 1] shows the characteristic variation of mining unit costs with the degree of fragmentation, or the maximum size of blocks obtained from blasting. From the figure, it can be seen that optimum breakage must correspond to the lowest total costs, but reducing drilling-blasting costs only does not achieve such an optimum solution. Methods of designing surface or underground blasting operations should comply with the optimization criterion, but this compliance is feasible only if a detailed mining system analysis is available. Therefore, predictions of costs of loading, transporting, and mechanical breakage of ore as a function of its size will define a narrow range of variation for drilling and blasting parameters in order to get the minimum total costs.

Jan 1, 1972

A statistical investigation of folding at Mount Isa disclosed similar patterns in both the shales and the "silica dolomite" zones. Analysis of these patterns yields 3 groups of folds fully developed north plunging folds, fully developed south plunging folds, and flexuresrepresenting stages of development of folds. Interpretation of results indicates that a regional force from a southerly direction was responsible for the folding.The general pattern of shearing is allied to that of folding, with the exception of bedding-plane shearing. Many shears resulted from continued application of force on folds which ruptured after overthrusting. Other shears resulted from rupture of the more incompetent shale members, without associated folding. The shear pattern is consistent with the theory of a regional force from a southerly direction.INTRODUCTIONThe notes on folding and shearing presented in this paper are part of a current study of the structural geology of Mount Isa.FOLDING 1Measurement of FoldsInvestigation of folding underground involved the measurement of plunge, strike and dip of the axial plane, and the order of magnitude of each fold, together with its location and the rock type. The total number of folds measured was 701, of which 411 occurred in shale areas and 290 within the "silica dolomite" zones. All folds measured are located on main levels, from 7 level to 13 level inclusive. The sections of the mine involved are the Black Star, Black Rock and Racecourse. Detailed investigation of folds on the upper levels (4, 5 and 6) has not yet been done, but observations there suggest...

Jan 1, 1961

By G W. Wilson, C Panidis

Potentially acid forming (PAF) waste rock contained in dumps formed as a result of open cut mining of metalliferous orebodies are conventionally sealed or covered using a near-saturated, low permeability compacted clay layer, protected with a mulch layer and/or vegetated growth medium. The purpose of the compacted clay layer is to limit oxygen diffusion and the infiltration of rainfall into the dump. Where the aerial extent of the PAF waste rock dump is large, or where suitable clayey material is in short supply, it may be difficult to source sufficient suitable clayey material to form the cover. The paper describes a laboratory-based investigation of combining inert waste rock and tailings to form an alternative seal or cover material. The inert waste rock was sourced from the trafficked surface of a non-acid forming (NAF) waste rock dump, with a maximum particle size of about 100 mm. This was combined with NAF thickener underflow tailings slurry in various mass ratios, and the resulting mixtures tested for their particle size distribution, compaction characteristics, soil water characteristics (relationship between suction and volumetric moisture content), and saturated hydraulic conductivity. The mixtures tested ranged in consistency from those dry enough to be compactable, to those with the consistency of wet concrete that lend themselves to placement without the need for compaction. The laboratory test results showed that the suitability of the mixtures as seal or cover materials is very dependent on the particle size distribution of the mixture, with well-graded mixtures having substantial fines performing best.

Jan 1, 2003

By C Li

Removal of gangue minerals from ilmenite concentrates can beaccomplished by relatively low temperature roasting in controlled gasatmospheres to selectively enhance the magnetic separationcharacteristics of the ilmenite. At roasting temperatures below 800¦C the magnetising reactions are often not consistent with phase equilibria considerations. Metastable phases can nucleate and control the roasting products. In weathered ilmenites the phase assemblages and microstructures in the altered ilmenite grains can influence the roasting reactions. In this paper we give an overview of the phase chemistry of chemically weathered ilmenites and of metastable phases formed by low temperature roasting. We also report the results of roast experiments conducted in a neutral gas atmosphere. Major increases in magnetic properties after short roasting times at low temperatures were obtained for a range of ilmenite concentrates. For example heating a secondary ilmenite concentrate from Western Australia for 15 minutes in nitrogen at 600¦C gave an increase in the three kilogauss magnetic fraction from three to 92 wt per cent. The solid state phase changes accompanying the inert atmosphereroasts were characterised by combining elemental analyses withquantitative phase analyses of the ilmenite concentrates and their roast products. It was found that the phase reaction that is principally responsible for the increase in the magnetic properties of weathered ilmenites involves a transformation of disordered ferrous-containing pseudorutile to an ordered ilmenite-hematite solid solution containing typically ten to 35 mole per cent of the hematite component. Examples are given of the application of the inert atmosphere roast to effect separations of ilmenite from gangue minerals.

Jan 1, 2001

By Richard P. Curtin, Madan M. Singh, Francis S. Kendorski

INTRODUCTION The use of roof and rock bolts to reinforce the strata is an established method of rock support in both underground and surface excavations. However, the need to drill a hole, extract the drill-rods, and then place the bolt is time-consuming and costly. This becomes even more significant if the bolting is repetitive and extensive as in coal mining. Though the main thrust of this development was directed towards coal mining, the basic concepts are also widely applicable to all excavations. The authors, therefore, feel that this innovation should be of interest in rapid excavation and in tunneling. In the case of coal mining, it has been established from past statistics that the roof-bolting operation is the most hazardous activity. This is primarily because of the operator being exposed to unsupported ground. It is evident that remote installation of roof bolts would markedly improve the safety of the operation, if accomplished more readily with self-drilling bolts rather than the conventional two-step variety operation. Thus, in addition to increasing productivity, this development can be considered to be a milestone towards further improvements. The objective of this program was to establish the technical and economic feasibility of self-drilling roof bolts for use in coal mines. It might be clarified at the outset that this work was, therefore, directed primarily at showing that workable self-drilling bolts with less cost can be developed, which could be effectively used in mines. It was not to fabricate a production model bolt.

Jan 1, 1979

By J. W. Leonard

One of the more obvious phenomena which relate to coke formation is that soft coals of low volatile matter content tend to yield hard or high strength cokes while hard coals of high volatile matter content tend to yield soft or low strength cokes. This observation led researchers of the Coal Research Bureau of West Virginia Univ. to study the possibility of using Hardgrove grindability as a supplemental rank indicator for coking properties. Grindability has been used for many years as a means to measure the resistance of coal to comminution but it has rarely if ever been considered for evaluating coals for carbonization. The coal proper- ties which are measured by grindability are complex, but recent work with the difficult-to-correlate high volatile coals has demonstrated that a 93% correlation exists between grindability and the total petrographic rnicrinites, exinites, and resinites. This work demonstrated that inherent ash had no apparent effect on the grindability of high volatile coals, suggesting that the coal substance is apparently harder than the associated ash. These observations, together with the patented Burstlein process," indicate that the distribution of hard and soft components in the individual high volatile coals and blends of coals may be quantitatively interrelated to coke stability through selected ranges of coal volatile matter. The objective of this progress report is 1) to demonstrate the statistical relationships which exist between coal grindability and the numerous coal petrographic entities and 2) to present the results of initial studies concerning the correlation of the coke physical strength index of stability with coal volatile matter and grindability.

Jan 3, 1964

By D. Harrington

TheRe has been, during the past year, a wealth of report data and discussion relating directly or indirectly to various phases of ventilation of metal mines, and many of the data are from foreign sources. The phase of the subject most generously accorded the attention of the technical press is that of cooling mine air, with much less attention to other fairly intimately associated features such as fan performance, friction factors, fires, mine gases, mine lighting, health of miners, and ventilation standards. Cooling Mine Air South Africa, with its very deep mining on the Rand and with fairly high working temperatures, 'contributes the most definite data on the subject of cooling mine air, and undoubtedly the most interesting issued are those from a paper by J. H. Dobson,' in which he gives a comprehensive review of the subject as gleaned largely by analyzing the data in three papers.2 Dr. Dobson's summation is decidedly interesting. In general it is recognized that the introducing into the mine and circulating to the working places of large volumes of pure air is the most effective method of giving deep, hot metal-mine workings reasonably efficient working conditions. A tabulation as to the cost of securing various amounts of cooling by circulating various volumes, from 230,000 to 760,000 cu. ft. per min., indicates that there are cost limits beyond which increase of quantity of air in circulation is impracticable, as the annual cost of circulating 230,000 cu. ft. of air per min. in a certain mine at a depth of

Jan 1, 1928

By John H. Duke

The success of most attempts to evaluate gold orebodies depends largely on the reliability and availability of representative sampling data and the accuracy of geological interpretation. An accurate prediction of the continuity of geology is paramount to a reliable prediction of gold reserves. Many of the problems encountered in gold mine evaluation and planning revolve around the difficulties in interpreting complex geology from sparse drilling data and the eagerness of mine financiers and promoters to start mining in order to derive an early cash flow. Following a program of sampling, geophysics, mapping and geological interpretation, a conceptual orebody model evolves in the minds of those working on the project. It is this model which is used typically in ore reserve computations and mine planning. Computer modelling techniques to represent and evaluate the conceptual model are now available. The main advantages of using computer modelling methods lie in being able to rapidly evaluate, modify and quantify the conceptual orebody model. Ore zones or domains can be recognised and defined both from geology and sampling results. Once these domains are defined as a series of boundaries, they may be modelled as two dimensional grid surfaces or as wire-framed three dimensional geometries, depending on the complexity of the orebody. It is the definition of these domains which provides the sound geological basis for reserves computation. To estimate reserves it is necessary to determine both volume of ore and grade of ore. The ore volume is calculated within each domain as defined by the confining surfaces or wire-frames. The ore

Jan 1, 1987

By E. M. Wise

IT is known qualitatively that the recrystallization behavior of platinum is dependent upon the amount and particularly the nature of impurities present, the amount of prior cold-work and the annealing time and temperature, but published data are limited. A study of the effects of cold-work and annealing temperature on the hardness of a sample of very pure platinum was undertaken to supply part of this information. CONCLUSIONS 1. The platinum used in the experiments had a probable platinum content of 99.99+ per cent, and had the following mechanical properties in the completely softened condition: Vickers hardness number, 39.4; ultimate tensile strength, 19,340 lb. per sq. in.; proportional limit, very low; elongation, 37.5 per cent in 2 inches. 2. The effect of cold-rolling on the hardness is shown in Fig. 1. The hardness increases rapidly up to 10 to 15 per cent reduction and more slowly up to about 75 per cent reduction, beyond which it increases more rapidly. 3. The recrystallization temperatures for a 15-min. anneal, after cold-rolling 19, 39.5, 50.8, 66, 80.5 and 89.5 per cent reduction in thickness, are approximately 765°, 700°, 635°, 600°, 545° and 425°C., respectively. 4. The recrystallized grain size of this platinum is a function of the percentage of cold reduction, being larger the lower the percentage of cold-work. 5. Little or no grain growth resulted from subjecting recrystallized samples to higher temperatures or annealing for longer times.

Jan 1, 1940

By Edmund Shaw

IN THE year just past there were produced in the United States about 170,000,000 tons of sand and gravel. Much of this was pit-run material used for gravelling roads and as railroad ballast on lines that did not carry heavy traffic. But more than half of it was marketed as washed and sized, or graded, material. The methods used for preparing sand and gravel for the market have long been used in ore dressing and, as in ore dressing, depend on differences in the specific gravity of two substances or in the size or weight of particles. But many changes in the design and operation of plants and machines have been necessary. In ore dressing, the concentrate is only a small part of the feed; in sand and gravel washing, it is much the larger part of the feed. In addition, such close work as is needed when con¬centrating a metallic ore is not needed when washing gravel; the ability to put through a large tonnage is more important, and sizing, which is only a preliminary process in ore dressing, is an end to be attained. Rock crushers are found in most sand and gravel plants and they are used to break up the larger pieces from the deposit (known as boulders and cobbles) which are removed by a scalping screen. The crusher discharge is usually sent back to the scalping screen, the perforations in this screen setting the maximum size of the finished product.

Jan 2, 1926

By L. L. Davis

The rapid increase in the use of pulvcrulent adsorptive materials in the so-called "contact filtration" process for decolorizing lubricating oils makes it desirable to consider some of the basic principles involved. The commercial methods and types of equipment now used arc fairly well known, having been extensively described in the trade journals. In spite of this very little has been published concerning the factors which must be considered in the selection of a process or of a decolorizing ing material. It is commonly understood that contact filtration more or less closely follows the laws of adsorption. These principles have been thoroughly drscribed by Gurwitsch.' The contacting of neutral mineral oils seems to be adsorptive in character and apparently follows Freundlich's law of adsorption which may be expressed by the formula: X = Color material adsorbed hy the clay. M = Amount of clay used. C = Concentration of color material after equilibrium. A and P = Constants for a given oil and clay. Fig. 1 shows the decolorization curve for a natural, dark colored cylin-der stock when contacted with various quantities of clay, curve R being made with natural Riverside Texas fuller's earth and T being made with an acid-treated clay from Texas. As the Tag-Robinson color is inversely proportional to the depth of color, the reciprocal of these colors ran be assumed to be a funct ion of the concentratlion of coloring matter. The values of and C' can, therefore., br calculated by using the reciprocal Tag-Robinson colors, and when these

Jan 1, 1928