Twelve reaction vessels (2) in two parallel rows are attached to a switch block (401). The switch block (401) comprises a reaction block (403) and twelve slide plates (404), which are arranged within it and which can be adjusted between an open position, a closed position and a further position. In the open position, access in straight line to the associated reaction vessel (2) is possible whereas in the closed position, the corresponding reaction vessel (2) is closed in a pressure-tight manner by the switch block (401). In the case of a positive pressure or depression in the reaction vessel (2), the corresponding slide plate (404) is pressed by this positive pressure or depression against the reaction block (403) or is drawn onto it. By means of this switch block (401), it is also possible to carry out processes in which high positive pressures are present in the reaction vessels (2).