In the demo, the only arcane spell I could get was Arcane Summon at Level 2 in the Tower of Magi. Your mage skill must be at 16(I think, however my game is a singleton, so he only had 14(I think) in mage skills + a Mage bracelet) You need a Dispel Barrier scroll or Piercing crystal to reach it however, and it is in a secret passage, to the left(West I guess) of the item shop(Not the potion shop) You also get a mind crystal that is next to the spell book (It's just energy pulse however)
[i'm still a new at Avernum, so I probably messed up somewhere in there]