A new mass spectrograph has been constructed entirely of glass except for the electrodes. Furthermore its design reduces thermal dissociation to a minimum. Using this apparatus the products of ionization in carbon dioxide have been studied. The primary ions are found to be CO₂⁺, CO⁺, O⁺ and C⁺ appearing at 14.4, 20.4, 19.6 and 28.3 volts respectively. There is also some O₂⁺ produced as a secondary product with an ionization potential of 20.0 volts. Except for CO₂⁺ minimum values for all the ionization potentials can be calculated and are found to agree within the limits of error with the observed values.