What does Boxing Day have to do with boxing?
1590s "fine or light," also "evaporating rapidly" (c.1600), from Middle French volatile, from Latin volatilis "fleeting, transitory, flying," from past participle stem of volare "to fly" (see volant). Sense of "readily changing, fickle" is first recorded 1640s. Volatiles in Middle English meant "birds, butterflies, and other winged creatures" (c.1300).
volatile vol·a·tile (vŏl'ə-tl, -tīl')
Evaporating readily at normal temperatures and pressures.
That can be readily vaporized.
Tending to violence; explosive, as of behavior.