A magical arrow of acid springs from the character's hand and speeds to its target. The character must succeed at a ranged touch attack to hit the character's target. The arrow deals 2d4 points of acid damage. There is no splash damage. For every three caster levels (maximum 18), the acid, unless somehow neutralized, lasts for another round, dealing another 2d4 points of damage for that round. At 3rd–5th level, the acid lasts for 2 rounds; at 6th–8th level, the acid lasts for 3 rounds; and so on, to a maximum of 7 rounds at 18th level.