Maintaining a 4-mm gap between the tips of the electrodes was essential to the achievement of the accuracy and precision that this approach is capable of producing. For coals, the effective matrix of the 'arced sample' was modified through the use of a lithium carbonate buffer. This modification of the sample matrix made the arced sample resemble the lithium carbonate matrix of the Spex calibration standards. The quantity of lithium carbonate relative to that of the sample was sufficient to control the fusion, vaporization, transport, and excitation processes. The concentration ranges for the elements determined by the dc arc spectrographic methods described in this work are summarized in table 1 .
Elements exhibiting the largest deviations are aluminum, calcium, manganese, and silicon.
Experience in the analyses of other coals, vitrinites, exinites, and inertinites indicates that the deviations for the elements observed here are random, rather than systematic. Only five of the eight Argonne Premium Coals were available for analysis when this method was developed. Because this method is labor intensive and the accuracy and precision for this method at the detection limits for a majority of the elements are no better than the other methods implemented in the analysis of these coals, the analyses of the other three coals were not carried out. Only 18 elements were determined in the 5 whole Argonne Premium Coals. The results of these analyses are shown in tables 3 and 4 .