ONCE THE TEST PORTION has been selected, we most often must perform a number of operations on it before the analyte content is ready for measurement. Usually the first of these is dissolution. What we mean generally by “dissolution” is the conversion of the total test portion into an aqueous solution of dissociated salts. However, even that definition fails to incorporate a number of important exceptions in metal and ore analysis. Sometimes the medium is nonaqueous, as in halogen-solvent treatment for inclusion isolation, and sometimes only the analyte is leached or distilled from the test portion. Some European workers prefer the term “decomposition” for the general process and subcategorize “dissolution” for low-temperature work like acid treatment and “opening out” for high-temperature techniques like molten salt fusions.