Which preposition to use with ac

in Occurrences 6%

n. 2) it is stated that the invitatory is not to be said in Officio Defunctorum per annum, excepto die Commemorationis omnium fidelium defunctorum, ac in die obitus seu depositionis defuncti et quandocunque dicuntur tres nocturni.

per Occurrences 1%

Serverum appellatio ex eo fluxit, quod imperatores nostri captivos vendere, ac per hoc servare, nec occidere solent.]

Which preposition to use with  ac