  We present in a simple terms the theory of the factorizing operator
introduced recently by Maillet and Sanches de Santos for the spin - 1/2 chains.
We obtain the explicit expressions for the matrix elements of the factorizing
operator in terms of the elements of the Monodromy matrix. We use this results
to derive the expression for the general scalar product for the quantum spin
chain. We comment on the previous determination of the scalar product of Bethe
eigenstate with an arbitrary dual state. We also establish the direct
correspondence between the calculations of scalar products in the F- basis and
the usual basis.
