early 15c., "a cleansing from impurity," from Latin expurgationem (nominative expurgatio), noun of action from past participle stem of expurgare "to cleanse out, purge, purify; clear from censure, vindicate, justify," from ex- "out" (see ex-) + purgare "to purge" (see purge (v.)). Sense of "a removal of objectionable passages from a literary work" first recorded in English 1610s. Related: Expurgatory.
1. Method: The expurgation rate of carbon particle, the building of hemolysin antibody was determined.