Show METHODS OF COAL MINE SAMPLING AND difference IN RESULTS OBTAINED coal analyses help to describe the character of coal as it lies in the ground or as it may be delivered to the user states N H snyder fuel engineer 6 department of interior in technical paper just issued by the bureau of mines mines there is a distinct difference between mine samples and delivered sain samples ples analyses of mine samples of coal are plentiful but available analyses of delivered coal are relatively few mine samples are collected according in to a standard method the sampler cuts a channel 2 by 6 inches or 3 by 4 inches from roof to floor in the face of the seam and excludes from sampling any partings more than three eighths of an inch thick and any lenses or concretions of sulphur or other impurities more than two inches in maximum diameter and one half of an inch thick analyses of m mine ne samples form a permanent or scientific record of the coal at the point sampled they are important in determining the character of the coal in any given mine or district these analyses when the samples are taken in a standardized manner are valuable to the operator when compared with analyses of delivered d vered coal they show him whether or not his mine is being efficiently worked or whether the coal is being properly prepared which involves the question whether he has suitable mechanical appliances for separating 6 the impurities in the purchase of coal mine samples san aples may serve as a sufficient guide to an experienced purchaser who has knowledge of the impurities in the seam and the degree to which these are eliminated in mining and preparing the coal to the average purchaser unacquainted with these details however dependence on mine samplings may be misleading the quality of coal indicated by the face samples can aarel rarely y if ever be obtained in the delivered coal certain impurities that are eliminated from the formally prepared mine sample may not be eliminated by the miner interested in getting out a large tonnage some of the roof and floor may also be included if these are soft or blakey some mine analyses particularly those taken from za geological 6 reports 2 may be either from outcrop coal or small workings not be ond the influence of weathering when coal prices are high and competition is lessened it is easy for the miner and the management to lower the standards of preparation of the coal and a return to rigid standards is always difficult in sampling delivered coal the bureau of mines follows a definite procedure A sample of not less than 1000 pounds is systematically collected by taking equal increments at regular intervals throughout the delivery while coal is being loaded or unloaded and by crushing and reducing this sample by successive stages to laboratory size in using analyses of samples of delivered coal one must recognize that coal is not of uniform size and that impurities puri ties are not uniformly distributed throughout the mass hence there will be some lariat variation on in the results of sampling and though the same mass of coal is sampled a number of times the analyses would not agree absolutely except by chance it is only when a considerable number of analyses representing a considerable tonnage mined over a period of time are available that the average value and range of variation of a particular coal become known with certainty with reasonable tolerance however for these variations delivered coal can be sampled accurately enough for all practical purposes delivered coal from any given mine amne may differ from day to day through variations v in in mining or preparing the coal hence a record of analysis of delivered coal for any one time should not be considered as a permanent record for the output may be greatly improved by new methods of mining and preparation or on the other hand the output may deteriorate through carelessness in mining preparation |