SRD:Acidic Blast (Epic Weapon Enhancement)
From D&D Wiki
|This material is published under the OGL|
On command, an acidic blast weapon drips acid (though this deals no damage to the wielder). On any hit, this acid splashes the creature struck, dealing +3d6 points of bonus acid damage. On a successful critical hit it instead deals +6d6 points of acid damage (or +9d6 if the critical multiplier is x3, or +12d6 if the critical multiplier is x4). Bows, crossbows, and slings with this special ability bestow the bonus acid damage upon their ammunition.