def _bubbleP(cls, T):
        """Using ancillary equation return the pressure of bubble point"""
        c = cls._blend["bubble"]
        Tj = cls._blend["Tj"]
        Pj = cls._blend["Pj"]
        Tita = 1-T/Tj

        suma = 0
        for i, n in zip(c["i"], c["n"]):
            suma += n*Tita**(i/2.)
        P = Pj*exp(Tj/T*suma)
        return P
Using ancillary equation return the pressure of bubble point