Abstract: Production of a glass body provided with a glass membrane is disclosed, for a chemical sensor, in which a displaceably mounted dip tube through which a gaseous medium can flow is dipped into a mass of molten glass and pulled out again to withdraw a gob which is then put into the desired shape by supply of the gaseous medium. The dip tube is inserted into a mount, which is connected to a displaceably supported carriage which is then displaced as far as a lower end position (P1), which is defined on the basis of an adjustment device such that when the carriage moves downward the dip tube dips into the molten glass, and upon the retraction of the carriage the dip tube withdraws a gob that is suitable for processing. After one or more withdrawals of a gob, the one-piece or multiple-piece adjustment device is readjusted manually or automatically by a certain amount, to compensate for changes in the level of the molten glass caused by the withdrawal of gobs.