We request GEM beamtime to study the structure of samples of sodium silicate glass with and without CO3 carbonate groups. The presence of CO3 carbonate groups in the glasses is a challenge to standard ideas about glass structure, because of the large valence of C-O bonds. By determining the environment of the CO3 groups we may be able to explain why CO2 cannot be dissolved in glasses below a certain modifier content (56 mol% Na2O for sodium silicate glasses), and yet beyond this composition the additional CO2 seems to be almost completely retained. It is unlikely that there are CO2 molecules trapped in the glass, but if they are there then the neutron diffraction results will have a good sensitivity to their presence. Dissolved CO2 in silicates (either as CO3 groups or CO2 molecules) is of particular geological interest.