In this work we will consider the extension of the classical arguments on the existence and conjugation of the Cartan subalgebras of a soluble Lie algebra. Also, a change in the classical terminology is presented taking into account the base of the modern presentation of the finite soluble groups classes. Finally we proof that the N-projectors of a finite dimensional soluble Lie algebra coincide with its Cartan subalgebras, where N is the class of all the nilpotentes Lie algebra.