Melf's Acid Arrow 
(Conjuration)

Range: 180 yds.
Components: V, S, M
Duration: Special
Casting Time: 2
Area of Effect: 1 target
Saving Throw: Special

 By means of this spell, the wizard creates a magical arrow that speeds to its target as if fired from the bow of a fighter of the same level as the wizard. No modifiers for range, nonproficiency, or specialization are used. The arrow has no attack or damage bonus, but it inflicts 2d4 points of acid damage (with saving throws for items on the target); there is no splash damage. For every three levels that the caster has achieved, the acid, unless somehow neutralized, lasts for another round, inflicting another 2d4 points of damage each round. So at 3rd-5th level, the acid lasts two rounds; at 6th-8th level, the acid lasts for three rounds, etc.
 The material components of the spell are a dart, powdered rhubarb leaf, and an adder's stomach.