What is the test for establishing that a subsequent confession at the station house was not impelled by the previous confession made by the appellant at the apartment where he was convicted of a similar crime?

Appellant's subsequent station house confession was not impelled by his earlier confession at the apartment. According to his own testimony he made the second confession in order to keep his wife out of prison so that she might return home and care for their baby daughter. This proof of an independent motive for this confession satisfied the People's burden of proving beyond a reasonable doubt that the causative link between the two confessions was broken. (See People v. Spencer, Supra, 66 Cal.2d 158, 168, 57 Cal.Rptr. 163, 424 P.2d 715, and the cases discussed and cited in fn. 8 thereof.)