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The equations of variance applicable to coal sampling can be solved only by substituting known values for each component of variance in the equations. The accuracy of analysis for dry ash content of coal is one contributing source of variation in the multiple system of variations which contribute complexity to a clear-cut solution of the coal sampling problem. This paper gives experimental data on the phase of the problem which embraces the variances associated with the reduction and analysis of the gross sample of coal after it has been collected. Variance values are included for each stage of the standard ASTM procedure for reduction and analysis as specified in Method D 271 - 48. The data indicate several points in the present procedure where systematic variations occur. Calculations of the magnitude of these systematic variations disclose the possible reduction of the variances in the reduction procedure and analysis if these systematic variations could be eliminated from the standard methods.
Anderson, W. W.
Technical Director, Commercial Testing and Engineering Co., Chicago, Ill.
Sutherland, M. L.
Assistant Professor of Statistics, Illinois Institute of Technology, Chicago, Ill.