The CO2 process has been recently introduced into foundry work and has very large potentialities and can be used in lieu of practically all dry sand molding and a large proportion of green sand molding. Instead of using sand bonded with natural clay, sodium silicate is mixed with silica sand and this is converted during gassing with CO2 to a form of silica which acts as the binder for the sand grains. The CO2 process enables existing pattern equipment to be employed and it has the advantage that greater accuracy can be achieved because the mould may be gassed, and thereby partially hardened before the pattern is withdrawn from the mould, reducing the amount of rap required to withdraw the pattern.