Abstract: The disclosure describes an apparatus for performing at least two successive chemical reactions in the same container. In order to successively carry out several chemical reactions in the same container (10), e.g. dosing uranium in the presence of plutonium and fission products, the container is placed in a working station above which issue tubes (16, 20) for supplying the products necessary for the reactions. When a product has to be introduced, a computer controls the descent of the corresponding tube. When the product may react inopportunely if it drops into the container (10) outside the time intended for this purpose, the lower end of the product supply tube (16) is automatically laterally displaced with respect to the container, when the tube is in the top position, e.g. by the cooperation of a pawl (102) with a slot (100) forming a cam.