The authors present long slit low dispersion flux calibrated spectra for the planetary nebula A 78, and from these they obtain the chemical abundances and their variation within the nebula. In the central part of the nebula almost no hydrogen is found implying that the envelope of the central star is burning helium. The authors also measured an over-abundance of processed material which has been convected from the centre of the star. In the outer part of the nebula the abundances are close to solar.