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Results of a sampling test made on a coal from one source using an automatic sampler that employs a slotted cylinder for the sampling instrument are presented and discussed. The test procedure and results are given in some detail for the purpose of assessing the procedure and to encourage others to perform and report similar tests. Automatic samples were removed at five different locations across the belt and are compared with hand samples taken at similar locations from the stopped conveyor belt. A statistical analysis of 11 tests shows that the coal varied from time to time and that the mean values from the different sampling locations were different. This was observed both in the case of hand samples and machine samples, with the machine samples indicating somewhat more variation from time to time, as might be expected, since they were taken at points more widely separated in the coal stream. The weight of sample collected by the automatic sampler tended to be much more uniform than the belt load (from position to position), indicating that a gross sample taken by machine, under these conditions, would not be properly proportioned. Size distribution of the machine samples was biased in the direction of including too many fines, that is, excluding coarse coal. The average ash of the two types of sample differed “significantly.” Since the difference was only 0.3 per cent, in this case, there may be no reason to be unduly perturbed, but the difference is real. A coal having another size or ash distribution, or both, and handled at a different tonnage per hour might show up better than this coal in the comparison of hand versus machine samples, but it is clear that under some conditions the comparisons could be much more unfavorable.
Blatter, A. O.
Chief Chemist, Union Electric Co., St. Louis, Mo.