For white dwarfs with effective temperatures smaller than 12000 K, the percentage of objects with a helium-rich atmosphere increases compared to the hydrogen-rich sequence. The carbon abundance, which can be determined from line and band strengths (Bues, 1973; Koester et al., 1982), varies by more than a factor of 1000 within this class. Moreover, for the subclass of white dwarfs with strong magnetic fields, the abundance ratio of H/He differs from that of the DB and DA sequences. The hot star Feige 7, analyzed by Liebert et al. (1977), shows lines of hydrogen and helium at a comparable strength for a moderately strong field of 103 Tesla. If there is any chance of finding white dwarfs which are descendants of hot, non-degenerate helium stars with rotation and magnetic fields, then it should be within these objects of mixed composition.