This test method is a relative measure of the degree of oxidation present in coal. It does not determine the quantitative amount of oxidized coal present. It is only intended to serve as a guide to the supplier, buyer, and user for selecting coals for metallurgical use.
Note 1—The values shown in Table 1 are based on the transmittance obtained using the original procedure (wavelength at 520 nm, 17-mm light path, 2– to 3-min boiling time, dilution of the extract to 80 mL). At these conditions, coals that had transmittance values greater than 90 % were considered to be unoxidized, coals less than 80 % were considered to be oxidized, and coals between 80 and 90 % were considered suspect. As this procedure becomes accepted as the standard and more experimental data are gathered, modifications to these cutoff values are expected. Note that lower rank bituminous coals are more easily extracted than higher rank coal.
